Call by Value

Call by Value means that Java passes a copy of the value to a method, not the original variable itself. Any changes made to the parameter inside the method do not affect the original variable in the caller. This is a frequently asked interview topic, especially to clarify the confusion around objects and references.

Is Java Call by Value or Call by Reference?

Java is strictly CALL BY VALUE. Always.

• For primitives → copy of the value is passed
• For objects → copy of the reference is passed
• The original reference itself is never passed

Call by Value with Primitive Types

Example

void change(int x) {
    x = 50;
}
public static void main(String[] args) {
    int a = 10;
    change(a);
    System.out.println(a);
}
          

Output:

10
          

Explanation

• a = 10
• Copy of a is passed to x
• Changes to x do NOT affect a

Call by Value with Object References (Very Important)

Example

void change(int[] arr) {
    arr[0] = 100;
}
public static void main(String[] args) {
    int[] a = {10, 20};
    change(a);
    System.out.println(a[0]);
}
          

Output:

100
          

Explanation

• Copy of reference a is passed
• Both references point to the same object
• Object content is modified
• Reference itself is not changed

Why This Is Still Call by Value

void change(int[] arr) {
    arr = new int[]{50, 60};
}

int[] a = {10, 20};
change(a);
System.out.println(a[0]); // 10
          

Explanation

• Reference copy is reassigned inside method
• Original reference a remains unchanged
• Confirms Java is not call by reference

Visual Understanding (Conceptual)

Primitive

a = 10
copy -> x = 10
          

Object

a ----> [10, 20]
copy of reference ----> [10, 20]
          

Both references point to same object, but reference itself is copied.

Common Misconception

• ❌ Java supports call by reference
• ❌ Objects are passed by reference
• ✔ Java passes everything by value
• ✔ For objects, the value is the reference

Call by Value vs Call by Reference (Conceptual)

Why Java Uses Call by Value

• Simpler and safer
• Avoids unintended side effects
• Improves security and predictability
• Easier memory management

Common Beginner Mistakes

• Expecting primitive values to change
• Thinking Java is call by reference
• Confusing object mutation with reference change
• Not understanding reference copying

Interview-Ready Answers

Short Answer

Java uses call by value, meaning a copy of the value is passed to methods.

Detailed Answer

In Java, all method arguments are passed by value. For primitive types, a copy of the actual value is passed. For objects, a copy of the reference is passed, allowing object modification but not reference reassignment. Java does not support call by reference.

Key Takeaway

Java is 100% call by value. Understanding how primitive values and object references are passed prevents bugs and clears one of the most common interview traps.