java 基础知识之遍历Map 方法集合

桃扇骨 2023-10-16 19:33 23阅读 0赞

package com.jackey.topic;
    
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.Iterator;
    import java.util.List;
    import java.util.Map;
    import java.util.Set;
    
    //循环遍历map的方法
    public class CircleMap {
     public static void main(String[] args) {
      Map<String, Integer> tempMap = new HashMap<String, Integer>();
      tempMap.put("a", 1);
      tempMap.put("b", 2);
      tempMap.put("c", 3);
      // JDK1.4中
      // 遍历方法一 hashmap entrySet() 遍历
      System.out.println("方法一");
      Iterator it = tempMap.entrySet().iterator();
      while (it.hasNext()) {
       Map.Entry entry = (Map.Entry) it.next();
       Object key = entry.getKey();
       Object value = entry.getValue();
       System.out.println("key=" + key + " value=" + value);
      }
      System.out.println("");
      // JDK1.5中,应用新特性For-Each循环
      // 遍历方法二
      System.out.println("方法二");
      for (Map.Entry<String, Integer> entry : tempMap.entrySet()) {
       String key = entry.getKey().toString();
       String value = entry.getValue().toString();
       System.out.println("key=" + key + " value=" + value);
      }
      System.out.println("");
    
      // 遍历方法三 hashmap keySet() 遍历
      System.out.println("方法三");
      for (Iterator i = tempMap.keySet().iterator(); i.hasNext();) {
       Object obj = i.next();
       System.out.println(obj);// 循环输出key
       System.out.println("key=" + obj + " value=" + tempMap.get(obj));
      }
      for (Iterator i = tempMap.values().iterator(); i.hasNext();) {
       Object obj = i.next();
       System.out.println(obj);// 循环输出value
      }
      System.out.println("");
    
      // 遍历方法四 treemap keySet()遍历
      System.out.println("方法四");
      for (Object o : tempMap.keySet()) {
       System.out.println("key=" + o + " value=" + tempMap.get(o));
      }
      System.out.println("11111");
    
      // java如何遍历Map <String, ArrayList> map = new HashMap <String,
      // ArrayList>();
      System.out
        .println("java  遍历Map <String, ArrayList> map = new HashMap <String, ArrayList>();");
      Map<String, ArrayList> map = new HashMap<String, ArrayList>();
      Set<String> keys = map.keySet();
      Iterator<String> iterator = keys.iterator();
      while (iterator.hasNext()) {
       String key = iterator.next();
       ArrayList arrayList = map.get(key);
       for (Object o : arrayList) {
        System.out.println(o + "遍历过程");
       }
      }
      System.out.println("2222");
      Map<String, List> mapList = new HashMap<String, List>();
      for (Map.Entry entry : mapList.entrySet()) {
       String key = entry.getKey().toString();
       List<String> values = (List) entry.getValue();
       for (String value : values) {
        System.out.println(key + " --> " + value);
       }
      }
     }
    }