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Java中HashMap集合的6種遍歷方式詳解

更新時間：2023年12月11日 09:42:27 作者：warybee

這篇文章主要介紹了Java中HashMap集合的6種遍歷方式詳解,HashMap?基于哈希表的?Map?接口實現(xiàn),是以?key-value?存儲形式存在,即主要用來存放鍵值對,HashMap?的實現(xiàn)不是同步的,這意味著它不是線程安全的,我們來看一下其遍歷方式,需要的朋友可以參考下

HashMap的6種遍歷方式

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表達(dá)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 單線程

    @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 多線程

@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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