对ArrayList进行排序的两种方式

古城微笑少年丶 2022-06-16 23:14 144阅读 0赞

**根据<c> java.util.Collections重载的两个sort方法，我们可以用两种方式来实现对ArrayList进行排序.**

** 1)  static  void   sort(List<T> list, Comparator<? super T> c)  实现<I>java.util.Comparator，创建实例作为参数**

**  2) static <T implements Comparable<? super T>> void sort(List<T> list) 要排序的类继承<I>java.lang.Comparable,不需创建实例。**

**这是第一种排序方法示例，类SortByName实现<I>java.util.Comparator接口里面的compare方法，只能实现按姓名排序。但是，如果我的对象一种排序规则满足不了怎么办呢？例如我的student既想要按年龄排的结果，也想要按姓名排的结果，那就只能在创建一个类SortByAge再重新Comparator里面的compare方法。你会从排序方式2）的代码中发现它没有这种优势。**

package com.lgy.test;
    import java.util.*;
    public class Test {
    //代码示例 static void	sort(List<T> list, Comparator<? super T> c)
     public static void main(String[] args) {
    
    		Student zlj = new Student("丁晓宇", 60);
    		Student dxy = new Student("吕洋", 60);
    		Student cjc = new Student("吕峰", 1);
    		Student lgc = new Student("刘武", 19);
    
    		List<Student> studentList = new ArrayList<Student>();
    
    		studentList.add(zlj);
    		studentList.add(dxy);
    		studentList.add(cjc);
    		studentList.add(lgc);
    
    		System.out.println("按年龄升序：");
    		Collections.sort(studentList, new SortByAge());//创建实例作为参数
    		
    		for (Student student : studentList) {
    			System.out.println(student.getName() + "***" + student.getAge());
    		}
    		System.out.println("按姓名排序：");
    		Collections.sort(studentList, new SortByName());
    		for (Student student : studentList) {
    			System.out.println(student.getName() + "***" + student.getAge());
    		}
    	}
    }
    
    class SortByAge implements Comparator {
    	public int compare(Object o1, Object o2) {
    		Student s1 = (Student) o1;
    		Student s2 = (Student) o2;
    		
    		 if (s1.getAge() > s2.getAge())
    		 return 1;
    		 return -1;
    		 //不用写s1.getAge()==s2.getAge()的情况
    	}
    }
    
    class SortByName implements Comparable {
    	public int compare(Object o1, Object o2) {
    		Student s1 = (Student) o1;
    		Student s2 = (Student) o2;
    		return s1.getName().compareTo(s2.getName());
    		
    	}
    }

package com.lgy.test;
    
    public class Student{
    	private int age;
    	private String name;
    
    	public Student(String name, int age) {
    		this.name = name;
    		this.age = age;
    	}
    
    	public int getAge() {
    		return age;
    	}
    
    	public void setAge(int age) {
    		this.age = age;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    }

**下面是第二种排序方式示例，不用创建实例，但是只能按照一种规则进行排序，也就是说，如果我们的对象只需要一种排序规则的话，可以用这种方式。理由很简单，实现Comparable接口，重写Compare方法里面只能按照一种规则排序。**

package com.lgy.test;
    import java.util.*;
    public class Test {
    	public static void main(String[] args) {
    //代码示例 static <T extends Comparable<? super T>> void sort(List<T> list) 
    		Student zlj = new Student("丁晓宇", 60);
    		Student dxy = new Student("吕洋", 60);
    		Student cjc = new Student("吕峰", 1);
    		Student lgc = new Student("刘武", 19);
    
    		List<Student> studentList = new ArrayList<Student>();
    
    		studentList.add(zlj);
    		studentList.add(dxy);
    		studentList.add(cjc);
    		studentList.add(lgc);
    
    
    		System.out.println("按年龄升序：");
    		 Collections.sort(studentList);
    		 //不需要创建实例作为参数，Student类已经实现Comparable,
    //		 但是一个类只能有一种排序规则，也就是说，要么按年龄排，要么按姓名排。
    		for (Student student : studentList) {
    			System.out.println(student.getName() + "***" + student.getAge());
    		}
    
    	}
    }

package com.lgy.test;
    
    public class Student implements Comparable {
    	private int age;
    	private String name;
    
    	public Student(String name, int age) {
    		this.name = name;
    		this.age = age;
    	}
    
    	public int getAge() {
    		return age;
    	}
    
    	public void setAge(int age) {
    		this.age = age;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	@Override
    	public int compareTo(Object o) {
    		Student s = (Student) o;
    		if (s.getAge() > this.getAge())
    			return 1;
    		else
    			return -1;
    	}
    }