StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p>The Java programming language passes arguments only by value, that is, you cannot change the argument value in the calling method from within the called method.</p> <hr> <p>However, when an object instance is passed as an argument to a method, the value of the argument is not the object itself but a reference to the object. You can change the contents of the object in the called method but not the object reference.</p> <hr> <p>To many people, this looks like pass-by-reference, and behaviorally, it has much in common with pass-by-reference. However, there are two reasons this is inaccurate.</p> <ul> <li><p>Firstly, the ability to change the thing passed into a method only applies to objects, not primitive values. </p></li> <li><p>Second, the actual value associated with a variable of object type is the reference to the object, and not the object itself. This is an important distinction in other ways, and if clearly understood, is entirely supporting of the point that the Java programming language passes arguments by value.</p></li> </ul> <hr> <pre><code>The following code example illustrates this point: 1 public class PassTest { 2 3 // Methods to change the current values 4 public static void changeInt(int value) { 5 value = 55; 6 } 7 public static void changeObjectRef(MyDate ref) { 8 ref = new MyDate(1, 1, 2000); 9 } 10 public static void changeObjectAttr(MyDate ref) { 11 ref.setDay(4); 12 } 13 14 public static void main(String args[]) { 15 MyDate date; 16 int val; 17 18 // Assign the int 19 val = 11; 20 // Try to change it 21 changeInt(val); 22 // What is the current value? 23 System.out.println("Int value is: " + val); 24 25 // Assign the date 26 date = new MyDate(22, 7, 1964); 27 // Try to change it 28 changeObjectRef(date); 29 // What is the current value? 30 System.out.println("MyDate: " + date); 31 32 // Now change the day attribute 33 // through the object reference 34 changeObjectAttr(date); 35 // What is the current value? 36 System.out.println("MyDate: " + date); 37 } 38 } </code></pre> <hr> <pre><code>This code outputs the following: java PassTest Int value is: 11 MyDate: 22-7-1964 MyDate: 4-7-1964 The MyDate object is not changed by the changeObjectRef method; however, the changeObjectAttr method changes the day attribute of the MyDate object. </code></pre>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload