mep集合

map集合

1：put增加
代码如下

Map map=new HashMap<>();map.put("zs", "12");map.put("ls", "32");map.put("ww", "14");map.put("mz", "35");//当集合中存在映射关系，后来的映射关系会覆盖前面的映射关系       map.put("zs", "32");输出结果：{ww=14, ls=32, zs=32, mz=35}

2:keyset
（1）拿到所有Key值，所以get(key)拿对应的value值

Map map=new HashMap<>();map.put("zs", "12");map.put("ls", "32");map.put("ww", "14");map.put("mz", "35");map.put("zs", "32");Set ketSet=map.keySet();for (String key : ketSet) {System.out.println(key+":"+map.get(key));}运行结果如下：ww:14ls:32zs:32mz:35       

3:entrSet拿到所有映射关系

map.put("zs", "12");map.put("ls", "32");map.put("ww", "14");map.put("mz", "35");map.put("zs", "32");Set> entry=map.entrySet();for (Entry entry2 : entry) {System.out.println(entry2.getKey()+":"+entry2.getValue());}运行结果如下：ww:14ls:32zs:32mz:35       

Map应用

(1)Treemap排序

	HashMap map=new HashMap<>();map.put(new student("zs", 12), "beij");map.put(new student("maz", 22), "shanhai");map.put(new student("ls", 32), "guangzhou");map.put(new student("ww", 42), "shenzhen");map.put(new student("zs", 12), "hanzhou");System.out.println(map.size());}//输出结果为//因为元素地址不同，还没有去重/所以输出5

（2）map集合去重
1：自然排序接口

package com.Liuyujian;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;public class TretMap {public static void main(String[] args) {TreeMap hs=new TreeMap<>();
//		    map.put(new student("zs", 12), "beijin");hs.put(new student("maz", 22), "shanhai");hs.put(new student("ls", 32), "guangzhou");hs.put(new student("ww", 42), "shenzhen");hs.put(new student("zs", 12), "hanzhou");
//		System.out.println(map.size());Set> entrySet=hs.entrySet();for (Entry entry2 : entrySet) {System.out.println(entry2.getKey().getAge()+entry2.getKey().getName()+":"+entry2.getValue());}}
}
class student implements Comparable{private String name;private  int age;public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public student(String name, int age) {this.name = name;this.age = age;}@Overridepublic int hashCode() {// TODO Auto-generated method stubreturn this.getName().hashCode()+this.getAge();}@Overridepublic boolean equals(Object obj) {// TODO Auto-generated method stubif(obj instanceof student) {student stu= (student)obj;return this.getName().equals(stu.getName())&& this.getAge()==stu.getAge();}return false;}@Overridepublic int compareTo(student o) {// TODO Auto-generated method stubint num=this.getAge()-o.getAge();if(num==0) {return this.getName().compareTo(o.getName());}return num;}}
//调用hasCode,equals,conpareto,Comparable方法
//输出结果如下
//12zs:hanzhou
//22maz:shanhai
//32ls:guangzhou
//42ww:shenzhen

2比较排序接口

package com.Liuyujian;
import java.util.Comparator;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;public class TretMap {public static void main(String[] args) {TreeMap hs=new TreeMap<>(new stuComp());
//		    map.put(new student("zs", 12), "beijin");hs.put(new student("maz", 22), "shanhai");hs.put(new student("ls", 32), "guangzhou");hs.put(new student("ww", 42), "shenzhen");hs.put(new student("zs", 12), "hanzhou");
//		System.out.println(map.size());Set> entrySet=hs.entrySet();for (Entry entry2 : entrySet) {System.out.println(entry2.getKey().getAge()+entry2.getKey().getName()+":"+entry2.getValue());}}
}
class student implements Comparable{private String name;private  int age;public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public student(String name, int age) {this.name = name;this.age = age;}@Overridepublic int hashCode() {// TODO Auto-generated method stubreturn this.getName().hashCode()+this.getAge();}@Overridepublic boolean equals(Object obj) {// TODO Auto-generated method stubif(obj instanceof student) {student stu= (student)obj;return this.getName().equals(stu.getName())&& this.getAge()==stu.getAge();}return false;}@Overridepublic int compareTo(student o) {// TODO Auto-generated method stubint num=this.getAge()-o.getAge();if(num==0) {return this.getName().compareTo(o.getName());}return num;}  
}
class stuComp implements Comparator{@Overridepublic int compare(student o1, student o2) {// TODO Auto-generated method stubint num=o1.getName().compareTo(o2.getName());if(num==0) {return o1.getAge()-o2.getAge();}return num;}}
//应用比较排序接口,那么自然排序接口作废
//输出结果为：
//32ls:guangzhou
//22maz:shanhai
//42ww:shenzhen
//12zs:hanzhou

3运用mepj集合统计字符出现的次数
(1)将指定的字符装进一个容器进行筛选，将字符串转换成一个字符数组
（2）当字符第一次出现的时候，意味着map集合找不到对应的value值，给他赋值为1，当字符第二次出现的时候给他对应的值加1

package com.Liuyujian;import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;
import java.util.TreeSet;import com.sun.javafx.collections.MappingChange.Map;public class Hreemap {public static void main(String[] args) {String str="sadfgfdsasdfghgfdsdfgjvcvfhgdczgfdvcx";getRepts(str);
}private static void getRepts(String str) {char[] charArray=str.toCharArray();TreeMap map=new TreeMap<>();for (char c : charArray) {Integer val=(Integer)map.get(c);if(val==null) {map.put(c, 1);}else {map.put(c, ++val);}}StringBuffer sb=new StringBuffer();Set> entryset=map.entrySet();for (Entry entry : entryset) {sb.append(entry.getKey()+"("+entry.getValue()+")");}System.out.println(sb.toString());}
}//运行结果如下
// a(2)c(3)d(7)f(7)g(6)h(2)j(1)s(4)v(3)x(1)z(1)

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