About local variables

About local variables （ Fallible ）

stay java Only the value is passed in the call , No address call .
Look at a case directly ：

• A() Methods will a Variables are added every time they are called 1;
• B() Methods will b Variables from lowercase b Put it in capital letters B;
• C() Methods will c[0] from "c" Change to "C";

public class Test3 {
    
    @Test
    public  void test() {
    
        int a = 0;
        char b = 'b';
        char[] c = {
    'c'};
        A(a);
        B(b);
        C(c);
        System.out.println("a Variable final ：" + a);
        System.out.println("--------------------------------------------------------");
        System.out.println("b Variable final ：" + b);
        System.out.println("--------------------------------------------------------");
        System.out.println("c[0] Variable final ：" + c[0]);

    }
    public void A(int a){
    
        if(a != 2){
    
            System.out.println(" Local a:" + a);
            a += 1;
            A(a);
        }
    }
    public void B(char b){
    
        b = 'B';
        System.out.println(" Local b:" + b);
    }
    public void C(char[] c){
    
        c[0] = 'C';
        System.out.println(" Local c:" + c[0]);
    }
}

Let's first look at the changes of local variables ：

Local variables can be found a,b,c Can change as required .
Let's look at the changes of member variables ：

You can find a,b Variables don't change , This also confirms that in java Only the value is passed in the call , No address call .
in other words ：

• For basic data types , It realizes value transmission , It's just a parameter , It will not change the original value .
• For reference data types , Operate on this reference , In fact, it is also equivalent to the operation of formal parameters , Will not change the original reference .
• however , As for the The properties of the reference When operating , amount to CPP Address calls in , You can change the value of the attribute of this reference .

summary

1、 For basic type parameters , Re assign parameters in the method body , It does not change the value of the original variable .

2、 For reference type parameters , Reassign references to parameters in the method body , It does not change the reference held by the original variable .

3、 Operation of parameters in the method body , It does not affect the value of the original variable .

4、 The method body operates on the attributes of the object pointed to by the parameter , Will change the attribute value of the object pointed to by the original variable .

Reference from ：Java Method by passing parameters to change the value of variables