HashMap、LinkedHashMap、TreeMap

 HashMap 是非线程安全的，无序的。

LinkedHashMap、TreeMap 是有序的

    public static void main(String[] args) {
	
	System.out.println("hashmap：根据哈希值取出");
	Map<String, String> hashMap = new HashMap<>();
		hashMap.put("a", "textA");
		hashMap.put("b", "textB");
		hashMap.put("c", "textC");
		hashMap.put("1", "text1");
	Iterator<Entry<String, String>> it = hashMap.entrySet().iterator(); 
	while(it.hasNext()){
	    Map.Entry<String, String> e = it.next();
	        System.out.println("Key: " + e.getKey() + ";   Value: " + e.getValue());  
	}	
	System.out.println("LinkedHashMap：取出的顺序跟放进去的顺序是一样的");
	Map<String,String> linkedHashMap = new LinkedHashMap<>();
        	linkedHashMap.put("a", "textA");
        	linkedHashMap.put("b", "textB");
        	linkedHashMap.put("c", "textC");
        	linkedHashMap.put("1", "text1");
	it = linkedHashMap.entrySet().iterator();
	while(it.hasNext()){
	    Map.Entry<String, String> e = it.next();
	    System.out.println("Key:"+e.getKey()+"; Value:"+e.getValue());
	}

	System.out.println("TreeMap：字典排序（根据的是Key不是Value）底层结构是： 红黑树");
	//
	Map<String,String> treeMap = new TreeMap<>();
        	treeMap.put("a", "textA1");
        	treeMap.put("b", "textB");
        	treeMap.put("c", "textC");
        	treeMap.put("1", "textA2");
    	it = treeMap.entrySet().iterator();
    	while(it.hasNext()){
    	    Map.Entry<String, String> e = it.next();
    	    System.out.println("Key:"+e.getKey()+"; Value:"+e.getValue());
    	}
	
    }

hashmap：根据哈希值取出
Key: a;   Value: textA
Key: 1;   Value: text1
Key: b;   Value: textB
Key: c;   Value: textC
LinkedHashMap：取出的顺序跟放进去的顺序是一样的
Key:a; Value:textA
Key:b; Value:textB
Key:c; Value:textC
Key:1; Value:text1
TreeMap：字典排序（根据的是Key不是Value）底层结构是： 红黑树
Key:1; Value:textA2
Key:a; Value:textA1
Key:b; Value:textB
Key:c; Value:textC