HashMap,LinkedHashMap,TreeMap使用代码_JAVA相关

HashMap,LinkedHashMap,TreeMap应用
来源：http://blog.csdn.net/hopezhangbo/article/details/8097645

共同点：
HashMap,LinkedHashMap,TreeMap都属于Map；Map&nbsp主要用于存储键(key)值(value)对，根据键得到值，因此键不允许键重复,但允许值重复。

不同点:
1.HashMap里面存入的键值对在取出的时候是随机的,也是我们最常用的一个Map.它根据键的HashCode值存储数据,根据键可以直接获取它的值，具有很快的访问速度。
&nbsp&nbsp&nbsp在Map&nbsp中插入、删除和定位元素，HashMap&nbsp是最好的选择。

2。TreeMap取出来的是排序后的键值对。但如果您要按自然顺序或自定义顺序遍历键，那么TreeMap会更好。

3.&nbspLinkedHashMap&nbsp是HashMap的一个子类，如果需要输出的顺序和输入的相同,那么用LinkedHashMap可以实现.

代码实例：

package com.lrm.study.testcase;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.TreeMap;
public class MapAppTest {
/**
* @Create on Nov 9, 2009 by lrm
*/
public static void main(String[] args) {
   // TODO Auto-generated method stub
   MapAppTest.noOrder();
   MapAppTest.hasOrder();
   MapAppTest.likedHashMap();
}
public static void noOrder() {
   System.out.println("------无序（随机输出------");
   Map map = new HashMap();
   map.put("1", "Level 1");
   map.put("2", "Level 2");
   map.put("3", "Level 3");
   map.put("4", "Level 4");
   map.put("F", "Level F");
   map.put("Q", "Level Q");
   Iterator it = map.entrySet().iterator();
   while (it.hasNext()) {
    Map.Entry e = (Map.Entry) it.next();
    System.out.println("Key: " + e.getKey() + ";   Value: "
      + e.getValue());
   }
}
// 有序(默认排序，不能指定)
public static void hasOrder() {
   System.out.println("------有序（但是按默认顺充，不能指定）------");
   Map map = new TreeMap();
   map.put("F", "Level F");
   map.put("7", "Level 1");
   map.put("8", "Level 2");
   map.put("4", "Level 3");
   map.put("4", "Level 4");
   map.put("Q", "Level Q");
   map.put("E", "Level E");
   Iterator it = map.entrySet().iterator();
   while (it.hasNext()) {
    Map.Entry e = (Map.Entry) it.next();
    System.out.println("Key: " + e.getKey() + ";   Value: "
      + e.getValue());
   }
}
public static void likedHashMap() {
   System.out.println("------有序（根据输入的顺序输出）------");
   Map map = new LinkedHashMap();
   map.put("F", "Level F");
   map.put("7", "Level 1");
   map.put("8", "Level 2");
   map.put("4", "Level 3");
   map.put("4", "Level 4");
   map.put("Q", "Level Q");
   map.put("E", "Level E");
   Iterator it = map.entrySet().iterator();
   while (it.hasNext()) {
    Map.Entry e = (Map.Entry) it.next();
    System.out.println("Key: " + e.getKey() + ";   Value: "
      + e.getValue());
   }
}
}

输入结果：

——无序（随机输出——
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp3
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbspF
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp2
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp4
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbspQ
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp1
——有序（但是按默认顺充，不能指定）——
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp4
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp1
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp2
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbspE
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbspF
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbspQ
——有序（根据输入的顺序输出）——
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbspF
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp1
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp2
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbsp4
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbspQ
Key:&nbsp&nbsp&nbspValue:&nbspLevel&nbspE