Map的五种遍历方法

Posted 2020-08-24 "啷个哩个啷"

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);
   }
  }
 }
}