一个简单的例子：
实体类A，含一个成员变量num
public class A {
private int num;
public A(int num){
this.num=num;
}
public void setNum(int num){
this.num=num;
}
public int getNum(){
return num;
}
}
测试类含有两个函数，用于操作实体A
public class Main {
public static void fun1(A a){
a.setNum(100);
}
public static void fun2(A a){
A b=new A(101);
a=b;
}
}
实例化A后，将A作为参数传递到fun中，查看执行结果
public static void main(String[] args) {
A a=new A(99);
System.out.println(a.getNum());
fun1(a);
System.out.println(a.getNum());
fun2(a);
System.out.println(a.getNum());
}
结果为：
99
100
100
