HashMap集合和TreeMap集合

---------------------------HashMap集合的遍历 /第一种 package ji_he;import java.util.*;public class Example16 {public static void main(String[] args) {// TODO Auto-generated method stubMap map=new HashMap();map.put(1, "Jack");map.put(2, "Rose");map.put(3, "Lucy");map.put(3, "Lucy");Set kSet=map.keySet();//获取键集合Iterator iterator=kSet.iterator();while (iterator.hasNext()) {Object key = iterator.next();Object value=map.get(key);System.out.println(key+":"+value);}}} ///第二种 package ji_he;import java.util.*;public class Example17 {public static void main(String[] args) {// TODO Auto-generated method stubHashMap map=new HashMap();map.put("1", "Jack");map.put("2", "Rose");map.put("3", "Lucy");map.put("3", "Lucy");Set entrySet=map.entrySet();Iterator iterator=entrySet.iterator();//获取Iterator对象while (iterator.hasNext()) {Map.Entry entry=(Map.Entry) (iterator.next());//获取集合中键值对的映射关系Object key = entry.getKey();//获取Entry的键值Object value=entry.getValue();System.out.println(key+":"+value);}}} -------------------------------------TreeMap集合 ///TreeMap集合的遍历 package ji_he;import java.util.*;public class Example20 {public static void main(String[] args) {// TODO Auto-generated method stubTreeMap tMap=new TreeMap();tMap.put("1", "Jack");tMap.put("2", "Rose");tMap.put("3", "Lucy");Set kSet=tMap.keySet();Iterator iterator=kSet.iterator();while (iterator.hasNext()) {Object key = (Object) iterator.next();Object values=tMap.get(key);System.out.println(key+":"+values);}}} //TreeMap集合自定义比较器package top.wthfeng.hello;import java.util.Comparator; import java.util.Map; import java.util.TreeMap;public class Map2Test{public static void main(String[]args){Map<String,String> map = new TreeMap<>(new Comparator<String>(){public int compare(String o1,String o2){return o2.compareTo(o1); //用正负表示大小值}});//以上4行可用下面一行lambda表达式代替//Map<String,String> map1 = new TreeMap<>((o1,o2)->o2.compareTo(o1));map.put("zdef","rfgh");map.put("asrg","zfg");map.put("rgd","dfgh");map.put("cbf","gddf");for(Map.Entry<String,String> entry:map.entrySet()){System.out.println("key:"+entry.getKey()+",:value:"+entry.getValue()); }} } //输出结果（倒序）： key:zdef,:value:rfgh key:rgd,:value:dfgh key:cbf,:value:gddf key:asrg,:value:zfg

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