Java 中的值傳遞和引用傳遞問題

public class Operation {
    int data = 50;

    void change(int data) {
        data = data + 100;
    }

    public static void main(String[] args) {
        Operation op = new Operation();
        System.out.println("before change: " + op.data);
        op.change(200);
        System.out.println("after change: " + op.data);
    }
}
 

點選檢視結果

before change: 50
after change: 50

public class Operation2 {
    int data = 50;

    void change(Operation2 op) {
        op.data = op.data + 100;
    }

    public static void main(String args[]) {
        Operation2 op = new Operation2();

        System.out.println("before change " + op.data);
        op.change(op);
        System.out.println("after change " + op.data);

    }
}
 

點選檢視結果

before change 50
after change 150

Dog 類

public class Dog {
    String name;

    Dog(String name) {
        this.name = name;
    }

    String getName() {
        return this.name;
    }

    void setName(String name) {
        this.name = name;
    }

    String getObjectAddress() {
        return super.toString();
    }
}
 

public class PassByValueExample {
    public static void main(String[] args) {
        Dog dog = new Dog("A");
        System.out.println(dog.getObjectAddress());
        System.out.println("************************");
        func(dog);
        System.out.println("************************");
        System.out.println(dog.getObjectAddress());
        System.out.println(dog.getName());
    }

    private static void func(Dog dog) {
        System.out.println(dog.getObjectAddress());
        dog = new Dog("B");
        System.out.println(dog.getObjectAddress());
        System.out.println(dog.getName());
    }
}

點選檢視結果

Java基礎加強.引數傳遞[email protected]
************************
Java基礎加強.引數傳遞[email protected]
Java基礎加強.引數傳遞[email protected]
B
************************
Java基礎加強.引數傳遞[email protected]
A

public class PassByValueExample1 {
    public static void main(String[] args) {
        Dog dog = new Dog("A");
        func(dog);
        System.out.println(dog.getName());
    }

    private static void func(Dog dog) {
        dog.setName("B");
    }
}

點選檢視結果

B