Java中集合类初探

今天深入学习Collection以及Map集合工具的各种常用类.
其中在学习LinkedHashMap是遇到了无法按访问时间排序.
经过研究后发现了问题在于若需要开启按访问时间排序,需要在LinkedHashMap的构造方法中使用

LinkedHashMap(int initialCapacity,              float loadFactor,              boolean accessOrder)

并且设置accessOrder设置为true
附上代码

package MapTest;import java.util.HashMap;import java.util.Iterator;import java.util.LinkedHashMap;import java.util.Map;import java.util.TreeMap;public class TestMap {public static void main(String[] args) {    Map<String, Integer> hashMap = new HashMap<String,Integer>() ;    hashMap.put("Smith", 30) ;    hashMap.put("Anderson", 31);    hashMap.put("Levis", 29);    hashMap.put("Cook",29);    System.out.println("Display entries in HashMap");    System.out.println(hashMap);        Map<String,Integer> treeMap= new TreeMap<String,Integer>(hashMap);    System.out.println("Display entries in treeMap ascending order of key");    System.out.println(treeMap);    /*此处使用LinkedHashMap的构造方法     *LinkedHashMap(int initialCapacity,     *             float loadFactor,     *             boolean accessOrder)     *             并设置accessOrder为true     */    LinkedHashMap<String,Integer> linkedHashMap = new LinkedHashMap<String, Integer>(16,0.75f,true);    /*向linkedHashMap中存入键值*/    linkedHashMap.put("Smith", 30) ;    linkedHashMap.put("Anderson", 31);    linkedHashMap.put("Levis", 29);    linkedHashMap.put("Cook",29);    /*打印出访问元素之前的linkedHashMap*/    System.out.println("Display entries in LinkedHashMap");    System.out.println(linkedHashMap);    /*使用get()方法访问linkedHashMap访问其中key为"Levis"的元素*/    System.out.println("Levis is age " + linkedHashMap.get("Levis"));    /*打印出经过访问后的linkedHashMap*/    System.out.println("Display entries in LinkedHashMap after get(Levis)");    System.out.println(linkedHashMap);    }}

附上输出结果

Display entries in HashMap
{Smith=30, Cook=29, Levis=29, Anderson=31}
Display entries in treeMap ascending order of key
{Anderson=31, Cook=29, Levis=29, Smith=30}
Display entries in LinkedHashMap
{Smith=30, Anderson=31, Levis=29, Cook=29}
Levis is age 29
Display entries in LinkedHashMap after get(Levis)
{Smith=30, Anderson=31, Cook=29, Levis=29}