java 值传递和引用传递详 解

最 近 遇到java 值传递和引用传递问题 ,做 了 一 个 小 小 的 测试,分享 一 下,先 看 代码:
package com.test.pass;


public class TestPass {

/**
* @param args
*/
public static void main(String[] args) {
int p1 = 9;
int p2 = 10;
TestPass t = new TestPass();
t.add(p1, p2);
System.out.println("p1 = "+p1);
System.out.println("p2 = "+p2);
//pass by value

TestBO bo = new TestBO(10,20);
t.add(bo);
System.out.println("bo.m = "+bo.getM());
System.out.println("bo.n = "+bo.getN());
//pass by reference

int[] ps = new int[2];
ps[0] = 1 ;
ps[1] = 2 ;

t.add(ps);
System.out.println("ps0 = "+ps[0]);
System.out.println("ps1 = "+ps[1]);
//pass by reference


String sp = "Hello";
t.testStr(sp);
System.out.println("sp1 = "+sp);
t.testStr2(sp);
System.out.println("sp2 = "+sp);
//pass by value
}


public void add(int a,int b){
a = 2;
b = 3;
System.out.println("a = "+a);
System.out.println("b = "+b);
}

public void add(TestBO bo){
bo.setM(2);
bo.setN(3);
System.out.println("a = "+bo.getM());
System.out.println("b = "+bo.getN());
}

public void add(int[] as){
as[0] = 10 ;
as[1] = 20 ;
System.out.println("as[0] = "+as[0]);
System.out.println("as[1] = "+as[1]);
}

public void testStr(String str){
str = "world";//equals String str = new String("world");
System.out.println("str1 = "+str);
}

public void testStr2(String str){

System.out.println("str2 = "+str.concat(" World!"));
System.out.println("str22 = "+str);
}


}

class TestBO{

private int m;
private int n;
public TestBO(int m,int n){
this.m = m;
this.n = n;
}
public int getM() {
return m;
}
public void setM(int m) {
this.m = m;
}
public int getN() {
return n;
}
public void setN(int n) {
this.n = n;
}



}


总结:
Java中进行方法调用的时候传递参数时，遵循值传递的原则：
1）基本数据类型(byte,short ,int ,long, float ,double，boolean，char)，传递的是数据的拷贝
2）引用数据类型，传递的是传递的引用地址的拷贝，而不是该对象本身

但是要注意一下String类 ,有点特别,上面代码可以看出不像引用传递,而是值传递特征,其实不然,str = "world" 相当于 str = new String("world");