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Java中HashMap集合的6种遍历方式详解

2023-12-11 09:40:06 作者：warybee

这篇文章主要介绍了Java中HashMap集合的6种遍历方式详解,HashMap 基于哈希表的 Map 接口实现,是以 key-value 存储形式存在,即主要用来存放键值对,HashMap 的实现不是同步的,这意味着它不是线程安全的,我们来看一下其遍历方式,需要的朋友可以参考下

HashMap的6种遍历方式

1 Foreach entrySet方式

     @Test
     public void test1(){
         HashMap<Integer,String> languages=new HashMap<>();
         languages.put(1,"java");
         languages.put(2,"C#");
         languages.put(3,"javascript");
         languages.put(4,"C");
         languages.put(5,"C++");
         for (Map.Entry<Integer,String> entry:languages.entrySet()) {
             log.info("key:"+entry.getKey());
             log.info("value:"+entry.getValue());
         }
     }

2 Foreach keySet方式

@Test
public void test2(){
    HashMap<Integer,String> languages=new HashMap<>();
    languages.put(1,"java");
    languages.put(2,"C#");
    languages.put(3,"javascript");
    languages.put(4,"C");
    languages.put(5,"C++");
    for (Integer key:languages.keySet()) {
        log.info("key:"+key);
        log.info("value:"+languages.get(key));
    }
}

3 Iterator EntrySet方式

@Test
public void test3(){
    HashMap<Integer,String> languages=new HashMap<>();
    languages.put(1,"java");
    languages.put(2,"C#");
    languages.put(3,"javascript");
    languages.put(4,"C");
    languages.put(5,"C++");
    Iterator<Map.Entry<Integer, String>> iterator = languages.entrySet().iterator();
    while (iterator.hasNext()){
        Map.Entry<Integer, String> next = iterator.next();
        log.info("key:"+next.getKey());
        log.info("value:"+next.getValue());
    }
}

4 Iterator KeySet方式

@Test
public void test4(){
    HashMap<Integer,String> languages=new HashMap<>();
    languages.put(1,"java");
    languages.put(2,"C#");
    languages.put(3,"javascript");
    languages.put(4,"C");
    languages.put(5,"C++");
    Iterator<Integer> iterator = languages.keySet().iterator();
    while (iterator.hasNext()){
        log.info("key:"+iterator.next());
        log.info("value:"+languages.get(iterator.next()));
    }
}

5 Lambda表达式

   @Test
    public void test5(){
        HashMap<Integer,String> languages=new HashMap<>();
        languages.put(1,"java");
        languages.put(2,"C#");
        languages.put(3,"javascript");
        languages.put(4,"C");
        languages.put(5,"C++");
        languages.forEach((k,v)->{
            log.info("key:"+k);
            log.info("value:"+v);
        });
    }

6 Stream API方式

Stream API 单线程

    @Test
    public void test6(){
        HashMap<Integer,String> languages=new HashMap<>();
        languages.put(1,"java");
        languages.put(2,"C#");
        languages.put(3,"javascript");
        languages.put(4,"C");
        languages.put(5,"C++");
        languages.entrySet().stream().forEach(entry->{
            log.info("key:"+entry.getKey());
            log.info("value:"+entry.getValue());
        });
    }

Stream API 多线程

@Test
    public void test7(){
        HashMap<Integer,String> languages=new HashMap<>();
        languages.put(1,"java");
        languages.put(2,"C#");
        languages.put(3,"javascript");
        languages.put(4,"C");
        languages.put(5,"C++");
        languages.entrySet().parallelStream().forEach(entry->{
            log.info("key:"+entry.getKey());
            log.info("value:"+entry.getValue());
        });
    }

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