java传值问题？

传参等同于赋值，原代码等同于

public class Demo {

    public static void main(String[] args) {
        int a = 1;
        Integer b = new Integer(1);
        
        int _a = a;
        Integer _b = b;
        _a = 1000;
        _b = 1000;
        
        System.out.println(a);
        System.out.println(b);
    }

}

修改的是 _a，_b 这两个参数，a，b 不受影响

所以 java 无法在方法里修改外部的局部变量，代替的做法是：修改数组元素、对象属性、类属性

public class Demo {
    
    static int c;

    public static void main(String[] args) {
        int[] a = new int[] { 1 };
        MutableInt b = new MutableInt(1);
        c = 1;
        Method1(a, b);
        System.out.println(a[0]);
        System.out.println(b.value);
        System.out.println(c);
    }

    public static void Method1(int[] a, MutableInt b) {
        a[0] = 1000;
        b.value = 1000;
        c = 1000;
    }

}

class MutableInt {

    int value;

    public MutableInt(int value) {
        this.value = value;
    }

}