java 有序的Map LinkedHashMap简介

无序的HashMap

我们知道HashMap是无需的，数据并不是按我们插入的顺序排序的，我们可以验证下

public class Test6 {

public static void main(String[] args) {

Map hashMap = new HashMap();

hashMap.put("name1", "value1");

hashMap.put("name2", "value2");

hashMap.put("name3", "value3");

Set> set = hashMap.entrySet();

Iterator> iterator = set.iterator();

while(iterator.hasNext()) {

Entry entry = iterator.next();

String key = (String) entry.getKey();

String value = (String) entry.getValue();

System.out.println("key:" + key + ", value:" + value);

}

}

}

可以看到输出结果并不是按数据插入的顺序的

key:name3, value:value3

key:name2, value:value2

key:name1, value:value1

有序的LinkedHashMap

要想实现有序的Map，我们可以用LinkedHashMap，下面验证一下，把原来代码的HashMap替换成LinkedHashMap

public class Test6 {

public static void main(String[] args) {

Map hashMap = new LinkedHashMap();

hashMap.put("name1", "value1");

hashMap.put("name2", "value2");

hashMap.put("name3", "value3");

Set> set = hashMap.entrySet();

Iterator> iterator = set.iterator();

while(iterator.hasNext()) {

Entry entry = iterator.next();

String key = (String) entry.getKey();

String value = (String) entry.getValue();

System.out.println("key:" + key + ", value:" + value);

}

}

}

可以看到输出结果为我们插入的顺序

key:name1, value:value1

key:name2, value:value2

key:name3, value:value3