帮忙解释一下java值传递与引用传递

    Java code:
public static void main(String[] args)
{
StringBuffer str1 = new StringBuffer("hello");
test(str1);
System.out.println("main : " + str1);
}
public static void test(StringBuffer str)
{
StringBuffer tempStr = new StringBuffer();

System.out.println("first : " + str);
str = str.append(" world");
System.out.println("second: " + str);
str = tempStr;
System.out.println("third : " + str);
}



结果为:
first : hello
second: hello world
third :
main  : hello world

后两个的打印结果是什么原因

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试了下  果然是这样    困惑....帮顶...

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Java code:
public static void test(StringBuffer str)
{
StringBuffer tempStr = new StringBuffer(); //构造一个tempStr的StringBuffer对象

System.out.println("first : " + str);//输出str，没有问题，肯定是hello
str = str.append(" world");//在hello后面连接" world"，并重新赋值给str，所以str现在是"hello world"
System.out.println("second: " + str); //输出"