一直记不住，这次必须得自己记录一下了，遇到就查，太浪费时间了....虽然真的很基础的问题....

1、code实现：

public class Main {

public static void main(String[] args){

//        Scanner scanner=new Scanner(System.in);//在线笔试

HashMap<Integer,Integer> map=new HashMap<Integer,Integer>();

map.put(1,2);

map.put(2,3);

map.put(3,4);

map.put(4,4);

    //<a href="/tag/huoqu/" target="_blank" class="keywords">获取</a>所有key
    Set<Integer> keys=map.keySet();
    Iterator<Integer> iterator1=keys.iterator();
    while (iterator1.hasNext()){
        System.out.print(iterator1.next() +",");
    }
    System.out.println();
    System.out.println("------------------------");

    //<a href="/tag/huoqu/" target="_blank" class="keywords">获取</a>所有value
    Collection<Integer> values=map.values();
    Iterator<Integer> iterator2=values.iterator();
    while (iterator2.hasNext()){
        System.out.print(iterator2.next()+",");
    }
    System.out.println();
    System.out.println("------------------------");

    //<a href="/tag/quchu/" target="_blank" class="keywords">去除</a>value中重复值,相同值仅仅保留一个
    Set<Integer> valuesSimple=new HashSet<Integer>();
    for(int i:values){
        valuesSimple.add(i);
    }
    Iterator<Integer> iterator3=valuesSimple.iterator();
    while (iterator3.hasNext()){
        System.out.print(iterator3.next()+",");
    }
}
}

2、输出结果：