小程序找错

Question

import java.util.Random;import java.util.*;import java.util.Comparator; import java.io.*; public class StuCompExample{                  public static void main(String[] args)throws IOException{                   List stus = new ArrayList();                   for(int i = 0 ; i < 15 ; i++){                            Student stu = new Student(generateStuName(),generateStuAge());                                 stus.add(stu);                         }                   System.out.println("  该集合刚刚被创建 !");                   printCollection(stus);                   System.out.println("该集合将要被排序 !");                   try{                            Collections.sort(stus,new StudentAgeComparator());                   }catch(Exception e){                            //System.out.println(e);                            new PrintStream("aaa.txt").println(e);                            e.printStackTrace(new PrintStream("bbb.txt"));                   }                   //Collections.sort(stus);                   printCollection(stus);                   System.out.println("下面要反序了  ");                   Collections.reverse(stus);                   printCollection(stus);                                      System.out.println("下面要打乱顺序了  ");                   Collections.shuffle(stus);                   printCollection(stus);                                                    System.out.println("下面是最大值");                   System.out.println(       Collections.max(stus,new StudentAgeComparator()));                                                                           System.out.println("下面是最小值");                     System.out.println(Collections.min(stus,new StudentAgeComparator()));         }                            public static String generateStuName(){                   char[] nc = new char[8];                   for(int i = 0 ; i < nc.length ; i ++){                            Random rand = new Random();                            int j = 0 ;                            if(rand.nextBoolean()){                                     j = rand.nextInt( (char)'Z'-(char)'A')+(char)'A';                            }else{                                     j = rand.nextInt( (char)'z'-(char)'a')+(char)'a';                            }                                                       nc[i] = (char)j;                                                    }                   return new String(nc);                     }                  public static int generateStuAge(){                   Random rand = new Random();                                          return rand.nextInt(10)+15 ;         }                          public static void printCollection(Collection c){                   System.out.println("------------------------------");                   Iterator it = c.iterator();                   while(it.hasNext()){                            System.out.println(it.next());                   }                   System.out.println("###############################");                   System.out.println();         }}
class Student implements Comparable {         int age ;         String name ;         Student(String name , int age ){                   this.age = age ;                   this.name = name ;         }                  public String toString(){                   return   name + "  同学   年龄为 "+ age ;         }          public int compareTo(Object obj){                               return this.name.compareTo(((Student)obj).name);         }                  public boolean equals(Object o){                   if(!(o instanceof Student)){                            return false ;                   }                   return ((Student)o).name==this.name && ((Student)o).age==this.age;         }}class StudentAgeComparator implements Comparator{         public int compare(Object obj1 ,Object obj2){                   Student stu1 = (Student)obj1 ;                   Student stu2 = (Student)obj2 ;                   return (stu1.age > stu2.age)?1:((stu1.age== stu2.age)?0:-1) ;                                }}
能正确运行，但是上面自己构建的tudentAgeComparator比较器为什么只要实现接口的一个方法，还有个equals方法没有实现，为什么会不出错

Answer 1

class StudentAgeComparator implements Comparator{         public int compare(Object obj1 ,Object obj2){                   Student stu1 = (Student)obj1 ;                   Student stu2 = (Student)obj2 ;                   return (stu1.age > stu2.age)?1:((stu1.age== stu2.age)?0:-1) ;                                }}
只看这个自定义的比较器，前面的东西都不要看了 ，前面就是有个student类，包括姓名和年龄两个属性，把student的多个对象放进ArrayList，现在要对这个ArrayList里面的内容排序
 Collections.sort(stus,new StudentAgeComparator());//就是这句话，排序没有使用默认的排序方式，而是自定义了一个比较器，这个比较器实现了Comparator接口中的一个方法，还有一个equals只字未提，但是Collections.sort(stus,new StudentAgeComparator())这个实例化了它却没有出错

Answer 2

你也可以自己定义equals方法如Hibernate uid相等及两个对象相等