Is parameter passing in Java based on value or reference?

Is the parameter passing method in Java passed by value or by reference?

In Java, parameter passing methods include both value passing and reference passing, depending on the type of the parameter.

1. Pass by Value
   Value passing refers to passing a copy of the actual parameters to the formal parameters of the method when the method is called. Changing the values ​​of formal parameters in a method does not affect the values ​​of actual parameters.

The sample code is as follows:

public class PassByValueExample {
    public static void main(String[] args) {
        int number = 10;
        modifyValue(number);
        System.out.println("Number after method call: " + number);
    }
    
    public static void modifyValue(int value) {
        value = 20;
        System.out.println("Value inside method: " + value);
    }
}

The output result is as follows:

Value inside method: 20
Number after method call: 10

In the above code, the modifyValue method accepts an integer type parameter value. Inside the method, change the value of value to 20 and print it out. However, when printing the value of number in the main method, it is found that number is still 10, indicating that changing the value of the formal parameter will not affect the value of the actual parameter. .

2. Pass by Reference
   Pass by reference means that when a method is called, the reference (memory address) of the actual parameter is passed to the formal parameter of the method. Modifying the object pointed to by the formal parameter in the method will change the state of the object referenced by the actual parameter.

The sample code is as follows:

public class PassByReferenceExample {
    public static void main(String[] args) {
        StringBuilder name = new StringBuilder("Alice");
        modifyName(name);
        System.out.println("Name after method call: " + name);
    }
    
    public static void modifyName(StringBuilder builder) {
        builder.append(" Smith");
        System.out.println("Name inside method: " + builder);
    }
}

The output result is as follows:

Name inside method: Alice Smith
Name after method call: Alice Smith

In the above code, the modifyName method accepts a StringBuilder Parameters of type builder. Inside the method, "Smith" is appended to the object pointed to by builder, and then printed out. When printing name in the main method, it was found that name changed to "Alice Smith", indicating that changing the value of the formal parameter will affect the object referenced by the actual parameter. status.

It should be noted that although there is reference passing in Java, Java does not provide a way to directly change the actual parameter value by reference. For example, you cannot change the reference of an actual parameter by assigning a new memory address to the formal parameter in the method.

To summarize, the parameter passing method in Java is determined based on the type of the parameter. For basic data types (such as int, char, etc.), value passing is used; for object types, reference passing is used. Passing by value simply operates on a copy of the actual parameter, while passing by reference operates on the object referenced by the actual parameter.

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