java，map集合

package org.hanqi.array;
import java.util.*;

public class Test3 {

    public static void main(String[] args) {
        // TODO 自动生成的方法存根
        Map<String,String> m=new HashMap<String,String>();
        m.put("0533", "淄博");
        m.put("0531","济南" );
        m.put("0532","青岛" );
        System.out.println("长度="+m.size());
        //m.put("0532","黄岛");
        System.out.println("长度="+m.size());
        m.put("0534", "青岛");
        m.put(null, null);
        System.out.println("长度="+m.size());
        //根据Key获取value
        System.out.println("0533="+m.get("0533"));
        //Key是否存在
        if(m.containsKey("0533"))
        {
            System.out.println("Key 0533已存在");
        }
        //value是否存在
        if(m.containsValue("淄博"))
        {
            System.out.println("淄博已存在");
        }
        //遍历
        for(String k:m.keySet())
        {
            System.out.println(k+"="+m.get(k));
        }
    

    }

}