What is the difference between pass by value and pass by reference in java

The difference between Java value transfer and reference transfer: 1. Transfer of basic data types; 2. Transfer of objects; 3. Modification of reference pointing. Detailed introduction: 1. Transfer of basic data types. For basic data types, Java uses value transfer. When a variable of a basic data type is passed as a parameter to a method, the value of the variable is actually transferred, not the value of the variable. Its reference, which means that modifications to this parameter in the method will not affect the value of the original variable; 2. Transfer of objects, for object references, the situation is different, etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

Parameter passing in Java is mainly divided into two types: value passing and reference passing. There are clear conceptual and behavioral differences between these two delivery methods.

First, understand the basic concepts:

1. Pass by Value: In value passing, a copy of the parameter is passed. Any modifications to the copy will not affect the original data.

2. Pass by Reference: In pass by reference, the reference address of the object is passed. Modifications to the reference directly affect the original data.

Let’s analyze the difference between these two transfer methods in depth:

1. Transfer of basic data types:

For basic data types (such as int, char, float, etc. ), Java uses value transfer. When you pass a variable of a primitive data type as a parameter to a method, the value of the variable is actually passed, not a reference to it. This means that modifications to this parameter within the method will not affect the value of the original variable.

For example:

public static void modify(int value) {  
    value = value + 1;  
}  
  
public static void main(String[] args) {  
    int a = 5;  
    modify(a);  
    System.out.println(a); // 输出：5，而不是6  
}

2. Transfer of objects:

For object references, the situation is different. When you pass an object reference as a parameter to a method, what is actually passed is the reference address of the object, not the object itself. This is called "pass by reference". In the method, you can modify the contents of the object through this reference, and this modification will affect the original object. However, you cannot change the pointer of a reference, that is, you cannot make a reference point to a new object.

For example:

public static void modify(StringBuilder builder) {  
    builder.append(" modified");  
}  
  
public static void main(String[] args) {  
    StringBuilder strBuilder = new StringBuilder("Hello");  
    modify(strBuilder);  
    System.out.println(strBuilder.toString()); // 输出："Hello modified"  
}

In the above example, although StringBuilder is an object, we only modify the content of the object through a reference, rather than letting the reference point to a new StringBuilder object. So this is still a special case of pass-by-value. You cannot use this reference in a method to change the object pointed to by the original strBuilder reference. That is, you cannot have strBuilder reference a new StringBuilder object.

3. Modify the reference point:

If you want to change the reference point in the method (that is, let a reference point to a new object), then Java does not support this approach. of. This is because one of Java's design philosophies is that all objects are passed by value, not just basic data types. This is also to prevent programmers from misusing references, thereby destroying the encapsulation of the object. For example:

public static void changeReference(StringBuilder builder) {  
    builder = new StringBuilder("Another object"); // 这是合法的，但并没有改变原始的builder引用所指向的对象。  
}

In this example, we just let the builder local variable point to a new StringBuilder object, but this will not change the object pointed to by the original builder reference. This behavior is closer to passing by value than passing by reference.

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