Metode pridobivanja in nastavljanja se pogosto uporabljajo v programiranju v Javi. Metode pridobivanja in nastavljanja v Javi se pogosto uporabljajo za dostop in manipulacijo vrednosti polj razreda. Običajno so polja razreda okrašena z zasebnim specifikatorjem dostopa. Tako se za dostop do njih uporabljajo specifikatorji javnega dostopa z metodama getter in setter.
Potreba po metodi pridobivanja in postavljanja
Lahko bi trdili, da razglasite polja razreda kot javna in odstranite metodi getter in setter. Vendar pa je tak slog kodiranja slab in lahko poljem razreda dodamo absurdno vrednost. Razumejmo to s pomočjo primera.
public class GetterSetterExample { public salary; public storeSalaryDB(int salary) { // code for storing the salary in the database } // main method public static void main(String argvs[]) { GetterSetterExample obj = new GetterSetterExample(); obj.salary = -50000; // storing salary in database obj.storeSalaryDB(salary); } } Opazite, da koda v zbirko podatkov shranjuje negativno plačo, ki je napačna. Organizacija nikoli ne pripiše negativne plače na račun zaposlenega. Do dodelitve absurdnega zneska spremenljivki plača se je zgodilo, ker je deklarirana s specifikatorjem javnega dostopa. Pravilen način za pisanje zgornje kode je:
public class GetterSetterExample { private salary; // a setter method that assign a // value to the salary variable void setSalary(int s) { if(s <0 ) { s="-s;" } this.salary="s;" a getter mehtod to retrieve the salary int getsalary() return this.salary; public storesalarydb(int salary) code for storing in database system.out.println('the ') main method static void main(string argvs[]) creating an object of class gettersetterexample obj="new" gettersetterexample(); obj.setsalary(-50000); obj.storesalarydb(salary); < pre> <p>Now, we can see better control over what we send to the database to store. Whenever the salary is negative, we are converting the salary into a positive value, and then we are sending it to the database to store. Thus, no matter what value we send to the setter method, the if-block of the setter method takes care of the absurd value and thus gives better control on the salary value.</p> <h2>Getter Setter Java Program</h2> <p> <strong>FileName:</strong> GetterSetterExample1.java</p> <pre> class Employee { // class member variable private int eId; private String eName; private String eDesignation; private String eCompany; public int getEmpId() { return eId; } public void setEmpId(final int eId) { this.eId = eId; } public String getEmpName() { return eName; } public void setEmpName(final String eName) { // Validating the employee's name and // throwing an exception if the name is null or its length is less than or equal to 0. if(eName == null || eName.length() <= 0) { throw new illegalargumentexception(); } this.ename="eName;" public string getempdesignation() return edesignation; void setempdesignation(final edesignation) this.edesignation="eDesignation;" getempcompany() ecompany; setempcompany(final ecompany) this.ecompany="eCompany;" for printing the values @override tostring() str="Employee: [id = " + getempid() ', name=" + getEmpName() + " , designation=" + getEmpDesignation() + " company=" + getEmpCompany() + " ]'; str; main class. class gettersetterexample1 method static main(string argvs[]) creating an object of employee final emp="new" employee(); details are getting set using setter methods. emp.setempid(107); emp.setempname('kathy'); emp.setempdesignation('software tester'); emp.setempcompany('xyz corporation'); displaying 'tostring()' method, which uses getter methods system.out.println(emp.tostring()); < pre> <p> <strong>Output:</strong> </p> <pre> Employee: [id = 107, name = Kathy, designation = Software Tester, company = XYZ Corporation] </pre> <h2>Bad Practices in Getter and Setter Methods</h2> <p>There are some common bad practices that people usually do when they deal with the getter and setter methods.</p> <h3>Bad Practice 1:</h3> <p>Using getter and setter for the variable that is declared with low restricted scope.</p> <pre> public salary; void setSalary(int s) { salary = s; } int getSalary() { return salary; } </pre> <p>It is evident that from the main method, one can directly access the variable salary, which is not only bad but also makes the presence of the getter and setter methods irrelevant.</p> <h3>Bad Practice 2:</h3> <p>Using an object reference in the setter method. Consider the following program.</p> <p> <strong>FileName:</strong> GetterSetterExample2.java</p> <pre> class ABC { private int[] val; void setVal(int[] arr) { this.val = arr; // line 7 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; i++) { system.out.print(this.val[i] + ' '); } main class public gettersetterexample2 method static void main(string argvs[]) instantiating the abc obj="new" abc(); int mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating value at 0th index mainarr[0]="-1;" system.out.println(); < pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 -1 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>References are a bit tricky to deal with! In the above code, at line 43, the value got updated at the 0th index for array mainArr[]. However, it also got reflected in the array val[]. It should not happen as val[] array is declared private; hence, it is expected that any code outside of the class ABC should not modify it. However, because of the references, everything is messed up. The setter method setVal() expecting a reference of an int array, and at line 7, the reference of the int arr[] is getting copied to val[]. Note that the reference variable arr[] is storing the reference of the array mainArr[]. Thus, we can say val[] is storing the reference of the mainArr[].</p> <p>Therefore, whatever we change in the mainArr[] also gets reflected in the val[] array, which violates the purpose of the setter method. Also, there is no meaning in adding the private access specifier to the val[] array; because one can change the value of the val[] array in the main method, which is evident by looking at the output.</p> <p>A better way of writing the above code is:</p> <p> <strong>FileName:</strong> GetterSetterExample3.java</p> <pre> class ABC { private int[] val; void setVal(int[] arr) { int size = arr.length; // allocating the memory as // per the array arr size val = new int[size]; // line 11 for(int i = 0; i <size; 17 53 i++) { copying the value one by into val array this.val[i]="arr[i];" line } for displaying present in void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + ' '); main class. public class gettersetterexample3 method static main(string argvs[]) instantiating abc obj="new" abc(); mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating at 0th index mainarr[0]="-1;" system.out.println(); again pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 3 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>In the above code, we are doing the deep copy of elements of the array arr[]. In line 11, we are creating an entirely new array. Thus, the val[] is not referring to the arr[]. Also, in line 17, only values of the element are getting copied. Therefore, when we change the value of the 0th element at line 53, the change is not reflected in the val[]. Thus, the above code respects the encapsulation of the private member variable val[].</p> <h3>Bad Practice 3:</h3> <p>Returning an object reference in the getter method. Observe the following program.</p> <p> <strong>FileName:</strong> GetterSetterExample4.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { // returning the reference return val; // line 9 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; 42 i++) { system.out.print(this.val[i] + ' '); } main class. public class gettersetterexample4 method static void main(string argvs[]) instantiating the abc obj="new" abc(); invoking getter and storing result int arr[]="obj.getVal();" display obj.display(); updating value at 0th index arr[0]="-1;" line system.out.println(); again < pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 -1 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> </p> <p>The above code is not handling the references properly. The getter method is returning the reference of the array. The arr[] is storing the reference of the array val[], which is declared private in the class ABC. Because of exposing the reference to the outer world, arr[] can manipulate the val[], and thus, the encapsulation of the class ABC is breached. The proper way to handle the above is:</p> <p> <strong>FileName:</strong> GetterSetterExample5.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + ' '); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;></pre></size;></pre></size;></pre></size;></pre></=></pre></0> Slabe prakse v metodah Getter in Setter
Obstaja nekaj običajnih slabih praks, ki jih ljudje običajno počnejo, ko imajo opravka z metodami pridobivanja in postavljanja.
chrome naslovna vrstica
Slaba praksa 1:
Uporaba getterja in setterja za spremenljivko, ki je deklarirana z nizkim omejenim obsegom.
public salary; void setSalary(int s) { salary = s; } int getSalary() { return salary; } Očitno je, da je z glavno metodo mogoče neposredno dostopati do variabilne plače, kar ni samo slabo, temveč tudi povzroči nepomembnost prisotnosti metod getter in setter.
Slaba praksa 2:
Uporaba sklicevanja na objekt v metodi nastavitve. Razmislite o naslednjem programu.
Ime datoteke: GetterSetterExample2.java
class ABC { private int[] val; void setVal(int[] arr) { this.val = arr; // line 7 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; i++) { system.out.print(this.val[i] + \' \'); } main class public gettersetterexample2 method static void main(string argvs[]) instantiating the abc obj="new" abc(); int mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating value at 0th index mainarr[0]="-1;" system.out.println(); < pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 -1 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>References are a bit tricky to deal with! In the above code, at line 43, the value got updated at the 0th index for array mainArr[]. However, it also got reflected in the array val[]. It should not happen as val[] array is declared private; hence, it is expected that any code outside of the class ABC should not modify it. However, because of the references, everything is messed up. The setter method setVal() expecting a reference of an int array, and at line 7, the reference of the int arr[] is getting copied to val[]. Note that the reference variable arr[] is storing the reference of the array mainArr[]. Thus, we can say val[] is storing the reference of the mainArr[].</p> <p>Therefore, whatever we change in the mainArr[] also gets reflected in the val[] array, which violates the purpose of the setter method. Also, there is no meaning in adding the private access specifier to the val[] array; because one can change the value of the val[] array in the main method, which is evident by looking at the output.</p> <p>A better way of writing the above code is:</p> <p> <strong>FileName:</strong> GetterSetterExample3.java</p> <pre> class ABC { private int[] val; void setVal(int[] arr) { int size = arr.length; // allocating the memory as // per the array arr size val = new int[size]; // line 11 for(int i = 0; i <size; 17 53 i++) { copying the value one by into val array this.val[i]="arr[i];" line } for displaying present in void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample3 method static main(string argvs[]) instantiating abc obj="new" abc(); mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating at 0th index mainarr[0]="-1;" system.out.println(); again pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 3 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>In the above code, we are doing the deep copy of elements of the array arr[]. In line 11, we are creating an entirely new array. Thus, the val[] is not referring to the arr[]. Also, in line 17, only values of the element are getting copied. Therefore, when we change the value of the 0th element at line 53, the change is not reflected in the val[]. Thus, the above code respects the encapsulation of the private member variable val[].</p> <h3>Bad Practice 3:</h3> <p>Returning an object reference in the getter method. Observe the following program.</p> <p> <strong>FileName:</strong> GetterSetterExample4.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { // returning the reference return val; // line 9 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; 42 i++) { system.out.print(this.val[i] + \' \'); } main class. public class gettersetterexample4 method static void main(string argvs[]) instantiating the abc obj="new" abc(); invoking getter and storing result int arr[]="obj.getVal();" display obj.display(); updating value at 0th index arr[0]="-1;" line system.out.println(); again < pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 -1 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> </p> <p>The above code is not handling the references properly. The getter method is returning the reference of the array. The arr[] is storing the reference of the array val[], which is declared private in the class ABC. Because of exposing the reference to the outer world, arr[] can manipulate the val[], and thus, the encapsulation of the class ABC is breached. The proper way to handle the above is:</p> <p> <strong>FileName:</strong> GetterSetterExample5.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;></pre></size;></pre></size;></pre></size;> Pojasnilo:
Z referencami je malo težko ravnati! V zgornji kodi je bila v vrstici 43 vrednost posodobljena pri 0. indeksu za matriko mainArr[]. Vendar se je odrazilo tudi v matriki val[]. To se ne bi smelo zgoditi, ker je matrika val[] razglašena za zasebno; zato se pričakuje, da ga nobena koda zunaj razreda ABC ne bi smela spreminjati. Zaradi referenc pa je vse popackano. Metoda nastavitve setVal() pričakuje referenco matrike int, v vrstici 7 pa se referenca int arr[] kopira v val[]. Upoštevajte, da referenčna spremenljivka arr[] shranjuje referenco matrike mainArr[]. Tako lahko rečemo, da val[] shranjuje referenco mainArr[].
Igralec Rekha
Zato se karkoli spremenimo v mainArr[], odraža tudi v matriki val[], kar krši namen nastavitvene metode. Prav tako ni smisla dodajati specifikatorja zasebnega dostopa v matriko val[]; ker lahko spremenite vrednost matrike val[] v glavni metodi, kar je razvidno s pogledom na izhod.
Boljši način pisanja zgornje kode je:
Ime datoteke: GetterSetterExample3.java
class ABC { private int[] val; void setVal(int[] arr) { int size = arr.length; // allocating the memory as // per the array arr size val = new int[size]; // line 11 for(int i = 0; i <size; 17 53 i++) { copying the value one by into val array this.val[i]="arr[i];" line } for displaying present in void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample3 method static main(string argvs[]) instantiating abc obj="new" abc(); mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating at 0th index mainarr[0]="-1;" system.out.println(); again pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 3 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>In the above code, we are doing the deep copy of elements of the array arr[]. In line 11, we are creating an entirely new array. Thus, the val[] is not referring to the arr[]. Also, in line 17, only values of the element are getting copied. Therefore, when we change the value of the 0th element at line 53, the change is not reflected in the val[]. Thus, the above code respects the encapsulation of the private member variable val[].</p> <h3>Bad Practice 3:</h3> <p>Returning an object reference in the getter method. Observe the following program.</p> <p> <strong>FileName:</strong> GetterSetterExample4.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { // returning the reference return val; // line 9 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; 42 i++) { system.out.print(this.val[i] + \' \'); } main class. public class gettersetterexample4 method static void main(string argvs[]) instantiating the abc obj="new" abc(); invoking getter and storing result int arr[]="obj.getVal();" display obj.display(); updating value at 0th index arr[0]="-1;" line system.out.println(); again < pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 -1 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> </p> <p>The above code is not handling the references properly. The getter method is returning the reference of the array. The arr[] is storing the reference of the array val[], which is declared private in the class ABC. Because of exposing the reference to the outer world, arr[] can manipulate the val[], and thus, the encapsulation of the class ABC is breached. The proper way to handle the above is:</p> <p> <strong>FileName:</strong> GetterSetterExample5.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;></pre></size;></pre></size;> Pojasnilo:
V zgornji kodi delamo globoko kopijo elementov matrike arr[]. V vrstici 11 ustvarjamo povsem novo matriko. Tako se val[] ne nanaša na arr[]. Poleg tega se v vrstici 17 kopirajo samo vrednosti elementa. Zato, ko spremenimo vrednost 0. elementa v vrstici 53, se sprememba ne odraža v val[]. Tako zgornja koda upošteva enkapsulacijo spremenljivke zasebnega člana val[].
instanceof v Javi
Slaba praksa 3:
Vrnitev reference objekta v metodi getter. Upoštevajte naslednji program.
razvrsti arraylist v Javi
Ime datoteke: GetterSetterExample4.java
class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { // returning the reference return val; // line 9 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; 42 i++) { system.out.print(this.val[i] + \' \'); } main class. public class gettersetterexample4 method static void main(string argvs[]) instantiating the abc obj="new" abc(); invoking getter and storing result int arr[]="obj.getVal();" display obj.display(); updating value at 0th index arr[0]="-1;" line system.out.println(); again < pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 -1 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> </p> <p>The above code is not handling the references properly. The getter method is returning the reference of the array. The arr[] is storing the reference of the array val[], which is declared private in the class ABC. Because of exposing the reference to the outer world, arr[] can manipulate the val[], and thus, the encapsulation of the class ABC is breached. The proper way to handle the above is:</p> <p> <strong>FileName:</strong> GetterSetterExample5.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;></pre></size;> Pojasnilo:
Zgornja koda ne obravnava pravilno referenc. Metoda getter vrne referenco matrike. Arr[] shranjuje referenco matrike val[], ki je razglašena za zasebno v razredu ABC. Zaradi izpostavljanja sklicevanja na zunanji svet lahko arr[] manipulira z val[] in tako je prekršena inkapsulacija razreda ABC. Pravilen način za ravnanje z zgoraj navedenim je:
Ime datoteke: GetterSetterExample5.java
class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \\' \\'); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;> Pojasnilo: V zgornji kodi referenca zasebnega polja ni poslana v zunanji svet. V metodi getter se ustvari nova matrika, katere referenca se pošlje glavni metodi. Zato, ko se vrednost pri 0. indeksu spremeni v vrstici 54, ta sprememba vpliva na matriko temp[], ne na zasebno matriko val[]. Tako se ohrani enkapsulacija razreda ABC, saj referenca matrike val[] ni izpostavljena zunanjemu svetu.
Opomba 1: Za primitivne tipe podatkov (int, char itd.) ni treba ustvariti kopije v metodah getter in setter, saj za primitivne tipe podatkov ni koncepta referenc.
Opomba 2: Tipi objektov nizov delujejo tudi na referencah. Vendar pa za razliko od zgornjih primerov ni treba skrbeti za reference niza, ki so izpostavljene zunanjemu svetu. To je zato, ker so nizi nespremenljivi. Torej, ko nekdo manipulira z nizom v glavni metodi (ali kjer koli drugje), se ustvari nov objekt String, prejšnji pa ostane nedotaknjen.
Ime datoteke: GetterSetterExample6.java
class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } Izhod:
The String is: Hello India! The String is: Hello India!