＋设为首页 ＋添加到收藏夹
代码;
public class PassByValue1 {
int i=0;
PassByValue1(int newValue) {
i=newValue;
}
static void changeInt(int value){
value=98;
System.out.println("value in changeInt()="+value);
}
static void changeObjRef(PassByValue1 obj){
obj=new PassByValue1(99);
System.out.println("obj.i in changeObjRef()="+obj.i);
}
static void changeObjAttr(PassByValue1 obj){
obj.i=100;
System.out.println("obj.i in changeObjAttr()="+obj.i);
}
public static void main(String[] args) {
int value=2;
System.out.println("value before changeInt()="+value);
changeInt(value);
System.out.println("value after changeInt()="+value);
PassByValue1 obj=new PassByValue1(2);
System.out.println("------------");
System.out.println("obj before changeObjRef()="+obj);
System.out.println("obj.i before changeObjRef()="+obj.i);
changeObjRef(obj);
System.out.println("obj.i after changeObjRef()="+obj.i);
System.out.println("obj after changeObjRef()"+obj);
System.out.println("------------");
System.out.println("obj before changeObjAttr()="+obj);
System.out.println("Obj.i before changeObjAttr()="+obj.i);
changeObjAttr(obj);
System.out.println("obj.i after changeObjAttr()="+obj.i);
System.out.println("obj agter changeObjAttr()="+obj);
}
}
结果：
value before changeInt()=2
value in changeInt()=98
value after changeInt()=2
------------
obj before changeObjRef()=passbyvalue1.PassByValue1@5d87b2
obj.i before changeObjRef()=2
obj.i in changeObjRef()=99
obj.i after changeObjRef()=2
obj after changeObjRef()passbyvalue1.PassByValue1@5d87b2
------------
obj before changeObjAttr()=passbyvalue1.PassByValue1@5d87b2
Obj.i before changeObjAttr()=2
obj.i in changeObjAttr()=100
obj.i after changeObjAttr()=100
obj agter changeObjAttr()=passbyvalue1.PassByValue1@5d87b2
如何理解以上结果？特别是
obj before changeObjRef()=passbyvalue1.PassByValue1@5d87b2
obj.i before changeObjRef()=2
obj.i in changeObjRef()=99
obj.i after changeObjRef()=2
obj after changeObjRef()passbyvalue1.PassByValue1@5d87b2
------------
obj before changeObjAttr()=passbyvalue1.PassByValue1@5d87b2
Obj.i before changeObjAttr()=2
obj.i in changeObjAttr()=100
obj.i after changeObjAttr()=100
obj agter changeObjAttr()=passbyvalue1.PassByValue1@5d87b2
public class PassByValue1
{
int i = 0;
PassByValue1(int newValue)
{
i = newValue;
}
static void changeInt(int value)
{
value = 98;
System.out.println("value in changeInt() = " + value);
}
static void changeObjRef(PassByValue1 obj)
{
obj = new PassByValue1(99);
System.out.println("obj.i in changeObjRef()=" + obj.i);
}
static void changeObjAttr(PassByValue1 obj)
{
obj.i = 100;
System.out.println("obj.i in changeObjAttr()=" + obj.i);
}
public static void main(String[] args)
{
int value=2;
System.out.println("value before changeInt()=" + value); // value = 2
changeInt(value); // changeInt() = 98 value 是局部变量，退出方法的时间，value分配的内存收回
System.out.println("value after changeInt()="+value); // value = 2 故 value = 2
PassByValue1 obj = new PassByValue1(2); //
System.out.println("------------"); //-------------
System.out.println("obj before changeObjRef()="+obj); // 地址A
System.out.println("obj.i before changeObjRef()="+obj.i); // obj.i = 2
changeObjRef(obj); // obj.i = 99 obj 在changeObjRef中重新分配了地址，
//要不你可以在方法中尝试一下，System.out.println(obj);你会发现地址变了，
//obj在方法中也是一个局部变量，退出方法的时间，内存收回
System.out.println("obj.i after changeObjRef()="+obj.i); // obj.i = 2 故obj.i 还是等于2
System.out.println("obj after changeObjRef()"+obj); //地址A 地址没有变，还是一开始
//PassByValue1 obj = new PassByValue1(2); 时间的地址
System.out.println("------------"); // --------
System.out.println("obj before changeObjAttr()="+obj); // 地址A 地址没有变，还是一开始
//PassByValue1 obj = new PassByValue1(2); 时间的地址
System.out.println("Obj.i before changeObjAttr()="+obj.i); // obj.i = 2 还是原来的obj.i = 2
changeObjAttr(obj); // obj.i = 100 obj.i 重新赋值了，
//这个时间也更新了obj 中的i 的值，并记录到obj中，obj没有重新new，是初始的时间的那个
//PassByValue1 obj = new PassByValue1(2);
System.out.println("obj.i after changeObjAttr()="+obj.i); //obj.i = 100 所以obj.i变成了 100
System.out.println("obj agter changeObjAttr()="+obj); // 地址A 地址没有变，还是一开始
//PassByValue1 obj = new PassByValue1(2); 时间的地址，没有重新new
}
}
http://expert.csdn.net/Expert/topic/1437/1437310.xml?temp=.699917
请看上面的贴子里我的回复。
