java - java中的值传递和引用传递

Question

我正在阅读有关java中的按值传递和按引用传递的文章，其中一些说Java仅遵循“按值传递”，其中一些说原语和对象之间存在一些差异。所以我写了以下示例代码。并输出也。请评论并分享确切的答案是什么。

我检查了 Int、String、StringBuffer 和 Employee 类，现在它仅作为 Employee 类的引用传递。

package test;
class Emp {
    public String name="";
    public int age=0;

    public Emp(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    public String toString() {
        return "Name: "+ this.name + "....Age: "+ this.age;

    }
}
public class Class1 {
    public Class1() {
        super();
    }

    public void doChange(int i) {
        i = i +10;
        System.out.println("Value of Integer in Method:>"+ i);
    }

    public void doChange(Emp i) {
        i.age=29;
        i.name="rishu";
        System.out.println("Value of Employee In Method "+i.toString());
    }

    public void doChange(String i) {
        i = i + " Hello";
        System.out.println("value of i->"+ i);
    }


    public static void main(String[] args) {
        int i =10;
        String str="XXX";
        Class1 c= new Class1();
        StringBuffer sb= new StringBuffer();
        Emp e= new Emp("abhi",28);       

        sb.append("ABC ");
        System.out.println("");
        System.out.println("Value of Integer before Method:->"+ i);
        c.doChange(i);
        System.out.println("Value of Integer after Method:->"+ i);
        System.out.println("");
        System.out.println("Value of String before Method:->"+ str);
        c.doChange(str);
        System.out.println("Value of Integer after Method:->"+ str);
        System.out.println("");
        System.out.println("Value of StringBuffer before Method:->"+ sb);
        c.doChange(sb.toString());
        System.out.println("Value of StringBuffer after Method:->"+ sb);
        System.out.println("");

        System.out.println("Value of Employee before Method:->"+ e.toString());
        c.doChange(e);
        System.out.println("Value of Employee after Method:->"+ e.toString());
    }
}

输出:

Value of Integer before Method:->10
Value of Integer in Method:>20
Value of Integer after Method:->10

Value of String before Method:->XXX
value of i->XXX Hello
Value of Integer after Method:->XXX

Value of StringBuffer before Method:->ABC 
value of i->ABC  Hello
Value of StringBuffer after Method:->ABC 

Value of Employee before Method:->Name: abhi....Age: 28
Value of Employee In Method Name: rishu....Age: 29
Value of Employee after Method:->Name: rishu....Age: 29

Answer 1

Java 仅支持值传递。

但是，对于对象来说，按值传递的是对象的引用。。不，这与引用传递不同。区别在于:

如果你这样做:

public void doChange(Emp i) {
    i = new Emp("changed!", 42);
}

它在方法外部绝对没有影响 - 因为引用i是方法外部使用的引用的副本。但是，它引用同一个对象，因此如果您使用引用来更改对象的字段，这些更改在方法外部是可见的。