Is Java "pass-by-reference" or "pass-by-value"?


One of the fundamental concepts in programming is how methods or functions handle parameters. In the case of Java, there has been a long-standing debate about whether Java is "pass-by-reference" or "pass-by-value". In order to understand this distinction, let's delve deeper into the concepts of pass-by-reference and pass-by-value and explore how they apply to Java.


In Java, when a method is called with arguments, the values of those arguments are copied and passed to the method parameters. This means that any changes made to the parameter values within the method do not affect the original values of the arguments outside the method. This behavior is known as "pass-by-value".

Let's take a look at an example:

public class PassByValueExample {
    public static void main(String[] args) {
        int number = 10;
        System.out.println("Number after method call: " + number);

    public static void updateNumber(int value) {
        value = 20; // modifying the value

In the above example, the variable "number" is assigned a value of 10 and is passed as an argument to the "updateNumber" method. Inside the method, the value is modified to 20. However, when we print the value of "number" after the method call, it remains unchanged at 10. This clearly demonstrates the pass-by-value behavior in Java.


Pass-by-reference is a different concept where the memory address of a variable is passed to a method instead of its value. This allows the method to directly modify the original variable's value. However, Java does not support pass-by-reference directly. Instead, it uses a workaround to achieve similar behavior.

Java provides objects and references to objects. When an object reference is passed as an argument to a method, a copy of the reference is created and passed to the method. This reference points to the same object in memory as the original reference. Therefore, changes made to the object within the method will be reflected in the original object outside the method. This can sometimes lead to the misconception that Java is pass-by-reference.

Let's see an example:

public class PassByReferenceExample {
    public static void main(String[] args) {
        StringBuilder name = new StringBuilder("John");
        System.out.println("Name after method call: " + name);

    public static void updateName(StringBuilder value) {
        value.append(" Doe"); // modifying the object

In this example, we have a StringBuilder object named "name" with an initial value of "John". The "updateName" method takes a reference to the StringBuilder object. Within the method, we use the reference to modify the object by appending " Doe" to it. When we print the value of "name" after the method call, we see that the original object is also modified to "John Doe". This demonstrates the behavior similar to pass-by-reference.


While Java uses pass-by-value for primitive types and object references, the behavior of object references can sometimes give the illusion of pass-by-reference. Understanding this distinction is crucial for writing efficient and correct programs in Java.