300.21找出Person中年龄最大的

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package 找出Person中年龄最大的;import java.util.*;public class T1 {public static void main(String[] args) {Map m1 = new TreeMap(); Person p1 = new Person("ylz",22);Person p2 = new Person("gyf",21);Person p3 = new Person("gyc",20);Person p4 = new Person("gjq",23);m1.put(p1,4);m1.put(p2,3);m1.put(p3,2);m1.put(p4,1);Iterator it = m1.entrySet().iterator();//while(it.hasNext()) {Map.Entry entry = (Map.Entry)it.next();System.out.println(entry.getKey());//}/*Set key = m1.keySet();  Iterator i1 = key.iterator();//迭代Kwhile(i1.hasNext()) {   Object k = i1.next();                         System.out.println(k);  }注意:这种遍历方法效率低，因为会遍历两次，效率较低*/}}class Person implements Comparable {int age;String name;Person() {}Person(String name,int age) {this.name = name;this.age = age;}   public String toString() {          return "User:"+name+" age="+age+" ";      }     public int compareTo(Object o) {          int age1 = this.age;          int age2 = ((Person)o).age;                    if(age1 < age2) {     //二叉树知识            return 1;          }else if(age1 == age2) {              return 0;          }else {              return -1;          }     }}

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