学习java之HashMap和TreeMap

　　HashMap和TreeMap是Map接口的两种实现，ArrayDeque和LinkedList是Queue接口的两种实现方式。下面的代码是我今天学习这四个数据结构之后写的。还是不熟悉，TreeMap中的其余构造方法我还没有实现，真搞不懂同样的数据结构用java却写的这么麻烦。。

package regexp;

import java.util.Collection;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.Set;
import java.util.TreeMap;

public class test {
    public static void main(String args[]) throws NoSuchElementException{
        //Queue接口的实现
        Queue<Integer> q = new LinkedList<Integer>();    //通过LinkedList实现Queue接口
//        Queue<Integer> q = new ArrayDeque<Integer>();    //通过LinkedList实现Queue接口
        for(int i=0;i<10;i++) {
            q.add(i+1);
        }
        System.out.printf("%d%n", q.size());
        q.element();
        System.out.printf("%d%n", q.element());
        if(q.isEmpty()) {
            System.out.printf("%s%n", "The ArrayDeque is empty");
        } else {
            System.out.printf("%d%n", q.peek());
        }
        
        System.out.printf("%d%n", q.size());
        Integer first = q.remove(),last = q.remove();
        System.out.printf("%d %d%n",first,last);
        System.out.printf("%d%n", q.size());
        
        //Map接口的实现
        Map<Integer,String> mp = new HashMap<Integer,String>();
        mp.put(1, "111");
        mp.put(2, "222");
        String tt = mp.put(3, "333");
        System.out.println(tt);        //null
        String tmp = mp.put(1, "444");
        System.out.printf("%s%n",tmp);        //111
        System.out.printf("The size of the map is %d.%n", mp.size());    //3
        for(int i=0;i<mp.size();i++) {
            System.out.printf("id=%d, value=%s%n",i+1,mp.get(i+1));
        }
        mp.remove(1);    //delete key=1
        
        Set<Integer> keys = mp.keySet();
        //foreach
        for(Integer num : keys) {
            System.out.printf(" %d", num);
        }
        //iterator
        Iterator<Integer> it1 = keys.iterator();
        while(it1.hasNext()) {
            System.out.printf(" %d", it1.next());
        }
        
        
        Collection<String> coll = mp.values();
        //foreach
        for(String s : coll) {
            System.out.printf(" %s", s);
        }
        //iterator
        Iterator<String> it2 = coll.iterator();
        while(it2.hasNext()) {
            System.out.printf(" %s", it2.next());
        }
        
        Set<Map.Entry<Integer, String>> ss = mp.entrySet();
        //foreach
        for(Map.Entry<Integer, String> pair : ss) {
            Integer num = pair.getKey();
            String value = pair.getValue();
            
            System.out.printf(" %s '+' id=%d, value=%s", pair,num,value);
        }
        //iterator
        Iterator<Map.Entry<Integer, String>> it3 = ss.iterator();
        while(it3.hasNext()) {
            System.out.printf(" %s", it3.next());
        }
        
        //TreeMap
        TreeMap<Integer,String> treemp = new TreeMap<Integer,String>(new myComparator());
        treemp.put(111,"111");treemp.put(222, "222");treemp.put(112,"112");treemp.put(113, "113");
        for(Map.Entry<Integer, String> pair : treemp.entrySet()) {
            Integer num = pair.getKey();
            String str = pair.getValue();
            System.out.printf(" %d:%s ", num,str);
        }
    }
}

class myComparator implements Comparator<Integer> {
    public myComparator() {
    }
    public int compare(Integer a,Integer b) {
        return a.compareTo(b);
    }
    
}

下面是运行出来的结果，友友们可以对照着看，有没有初学者呀，come here and leave a message please!

10
1
1
10
1 2
8
null
111
The size of the map is 3.
id=1, value=444
id=2, value=222
id=3, value=333
 2 3 2 3 222 333 222 333 2=222 '+' id=2, value=222 3=333 '+' id=3, value=333 2=222 3=333 111:111  112:112  113:113  222:222