java - 从 itr.next() 返回的对象中打印成员

Question

以下代码存在编译问题。编译错误也附上。请提出相同的解决方案。

代码:

import java.util.*;

class test{

    int key;

    public static void main(String []args){
        test obj = new test();
        obj.key = 9999;

        LinkedList al = new LinkedList();
        al.add(obj);

        Iterator itr = al.iterator();
        while(itr.hasNext()){
            test temp = new test();
            temp = itr.next();
            System.out.println(temp.key);
        }   
    }
}

编译错误:

test.java:17: error: incompatible types

temp = itr.next(); ^

required: test

found: Object

Answer 1

有两种解决方案:

旧解决方案(Java 1.5 之前):

public static void main(String []args){
    test obj = new test();
    obj.key = 9999;

    LinkedList al = new LinkedList();
    al.add(obj);

    Iterator itr = al.iterator();
    while(itr.hasNext()){
        test temp = new test();
        // use type cast
        temp = (test) itr.next();
        System.out.println(temp.key);
    }   
}

通用解决方案(Java 1.5 及更高版本):

public static void main(String []args){
    test obj = new test();
    obj.key = 9999;

    LinkedList<test> al = new LinkedList<test>();
    al.add(obj);

    Iterator<test> itr = al.iterator();
    while(itr.hasNext()){
        test temp = new test();
        // use Generic
        temp = itr.next();
        System.out.println(temp.key);
    }   
}