java 基础知识之遍历Map 方法集合分析

熊孩纸 阅读:238 2021-03-31 23:32:23 评论:0
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); 
   } 
  } 
 } 
} 

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