比较器（Comparable与Comparator接口）

有错之处，希望大家可以指出来，谢谢。

概念

比较器：对两个或多个数据进行比较，以确定它们是否相等，或确定他们之间的大小关系以及排列顺序(来自于百度)。

Java中的比较器主要是通过实现Comparable与Comparator两个接口来实现的

Comparable接口

通过类继承接口，在类中对CompareTo()方法进行复写完成比较

主要实现语句：

类+implements Comparable<>{

…

public int compareTo(Work o){

return 0;

}

}

比较方法：

通过if(){}else{}语句进行判断返回值是-1,1,0中的哪一个，使用时通过返回的是-1，1，0来对比较者进行顺序的排列。

Comparable接口实现注意：接口的实现位置要在类所在的位置，比如此类是Worker类那么Comparable接口要在Worker类中实现。

例如：

 public class Worker implements Comparable<Worker> {
    
  ......
  ......
      
     public int compareTo(Worker o) {
    
        if (this.salary <o.salary) {
    
            return 1;
        } else if (this.salary>o.salary) {
    
            return -1;
        } else  {
       //如果第一个条件相等，的比较第二个条件
            if (this.age > o.age) {
    
                return 1;
            } else if (this.age < o.age) {
    
                return -1;
            } else{
    
                return 0;
            }

        }
 }

Comparable接口实例：

public class Worker implements Comparable<Worker> {
    
//public class Worker {
    
    private String name;
    private int age;
    private float salary;

    public Worker(String name, int age, float salary) {
    
        this.name = name;
        this.age = age;
        this.salary = salary;
    }

    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 float getSalary() {
    
        return salary;
    }

    public void setSalary(float salary) {
    
        this.salary = salary;
    }

    @Override
    public String toString() {
    
        return "Worker{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", salary=" + salary +
                '}';
    }
    @Override
    public int compareTo(Worker o) {
    
        if (this.salary <o.salary) {
    
            return 1;
        } else if (this.salary>o.salary) {
    
            return -1;
        } else  {
    
            if (this.age > o.age) {
    
                return 1;
            } else if (this.age < o.age) {
    
                return -1;
            } else{
    
                return 0;
            }

        }

    }
}

import java.util.*;

public class WorkerTest extends Worker{
    
    public WorkerTest(String name, int age, float salary) {
    
        super(name, age, salary);
    }

    public static void main(String[] args) {
    
        List<Worker> list =new ArrayList();
        list.add(new Worker("张三",30,9000));
        list.add(new Worker("李四",31,12000));
        list.add(new Worker("王五",28,9000));
        list.add(new Worker("王三",23,9000));
        list.add(new Worker("王二",26,12000));
        list.add(new Worker("王六",30,12000));
        list.add(new Worker("李美丽",48,12000));
        list.add(1,new Worker("赵六",26,3300));

        for(int i=0;i<list.size();i++){
    
            if (list.get(i).getName().equals("王五")){
    
                list.remove(i);
            }
        }

        for(int i=0;i<list.size();i++){
    
            System.out.println(list.get(i));
        }

// //迭代器
// Iterator<Worker> it=list.iterator();
// while(it.hasNext()){
    
// Worker s=it.next();
// System.out.println(s);
// }


       Collections.sort(list);  //ComparableTo
        //用sort方法排序，排序的条件是写在ComparaTo中的条件
        
        System.out.println("排序后");
        Iterator<Worker> it1=list.iterator();
        while(it1.hasNext()){
    
            Worker s=it1.next();
            System.out.println(s);
        }
    }
}

执行结果:

Worker{name='张三', age=30, salary=9000.0}
Worker{name='赵六', age=26, salary=3300.0}
Worker{name='李四', age=31, salary=12000.0}
Worker{name='王三', age=23, salary=9000.0}
Worker{name='王二', age=26, salary=12000.0}
Worker{name='王六', age=30, salary=12000.0}
Worker{name='李美丽', age=48, salary=12000.0}
排序后
Worker{name='王二', age=26, salary=12000.0}
Worker{name='王六', age=30, salary=12000.0}
Worker{name='李四', age=31, salary=12000.0}
Worker{name='李美丽', age=48, salary=12000.0}
Worker{name='王三', age=23, salary=9000.0}
Worker{name='张三', age=30, salary=9000.0}
Worker{name='赵六', age=26, salary=3300.0}

Comparator(比较器)接口

主要实现语句：

类+implements Comparator<>{

…

public int compare(Worker o1,Worker o2){

return 0;

}

}

比较方法：

通过if(){}else{}语句进行判断返回值是-1,1,0中的哪一个，使用时通过返回的是-1，1，0来对比较者进行顺序的排列。

Comparator接口实现注意：接口的实现位置要不在类所在的位置，比如此类是Worker类那么Comparable接口不能在Worker类中实现。

Comparator接口的设计符合OCP原则。

例如：

public class Worker {
    
    private String name;
    private int age;
    private float salary;

    public Worker(String name, int age, float salary) {
    
        this.name = name;
        this.age = age;
        this.salary = salary;
    }

    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 float getSalary() {
    
        return salary;
    }

    public void setSalary(float salary) {
    
        this.salary = salary;
    }

    @Override
    public String toString() {
    
        return "Worker{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", salary=" + salary +
                '}';
    }
}

import java.util.Comparator;

public class WorkerComparator implements Comparator<Worker> {
    
    @Override
    public int compare(Worker o1, Worker o2) {
    
        if (o1.getSalary() < o2.getSalary()) {
    
            return 1;
        } else if (o1.getSalary() > o2.getSalary()) {
    
            return -1;
        } else {
    
            if (o1.getAge() > o2.getAge()) {
    
                return 1;
            } else if (o1.getAge() < o2.getAge()) {
    
                return -1;
            } else {
    
                return 0;
            }

        }
    }

}

Comparator接口实例

public class Worker {
    
    private String name;
    private int age;
    private float salary;

    public Worker(String name, int age, float salary) {
    
        this.name = name;
        this.age = age;
        this.salary = salary;
    }
    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 float getSalary() {
    
        return salary;
    }
    public void setSalary(float salary) {
    
        this.salary = salary;
    }
    @Override
    public String toString() {
    
        return "Worker{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", salary=" + salary +
                '}';
    }
}

import java.util.Comparator;

public class WorkerComparator implements Comparator<Worker> {
    
    @Override
    public int compare(Worker o1, Worker o2) {
    
        if (o1.getSalary() < o2.getSalary()) {
    
            return 1;
        } else if (o1.getSalary() > o2.getSalary()) {
    
            return -1;
        } else {
    
            if (o1.getAge() > o2.getAge()) {
    
                return 1;
            } else if (o1.getAge() < o2.getAge()) {
    
                return -1;
            } else {
    
                return 0;
            }

        }
    }

}

import java.util.*;

public class WorkerTest extends Worker{
    
    public WorkerTest(String name, int age, float salary) {
    
        super(name, age, salary);
    }

    public static void main(String[] args) {
    
        List<Worker> list =new ArrayList();
        list.add(new Worker("张三",30,9000));
        list.add(new Worker("李四",31,12000));
        list.add(new Worker("王五",28,9000));
        list.add(new Worker("王三",23,9000));
        list.add(new Worker("王二",26,12000));
        list.add(new Worker("王六",30,12000));
        list.add(new Worker("李美丽",48,12000));
        list.add(1,new Worker("赵六",26,3300));

        for(int i=0;i<list.size();i++){
    
            if (list.get(i).getName().equals("王五")){
    
                list.remove(i);
            }
        }

        list.sort(new WorkerComparator());//Comparator
        System.out.println("排序后");
        Iterator<Worker> it1=list.iterator();
        while(it1.hasNext()){
    
            Worker s=it1.next();
            System.out.println(s);
        }
    }
}

执行结果：

Worker{name='张三', age=30, salary=9000.0}
Worker{name='赵六', age=26, salary=3300.0}
Worker{name='李四', age=31, salary=12000.0}
Worker{name='王三', age=23, salary=9000.0}
Worker{name='王二', age=26, salary=12000.0}
Worker{name='王六', age=30, salary=12000.0}
Worker{name='李美丽', age=48, salary=12000.0}
排序后
Worker{name='王二', age=26, salary=12000.0}
Worker{name='王六', age=30, salary=12000.0}
Worker{name='李四', age=31, salary=12000.0}
Worker{name='李美丽', age=48, salary=12000.0}
Worker{name='王三', age=23, salary=9000.0}
Worker{name='张三', age=30, salary=9000.0}
Worker{name='赵六', age=26, salary=3300.0}

也可以使用匿名内部类对Comparator和Comparable接口进行简化

TreeSet<Users> U=new TreeSet(new Comparator<Users>(){
    
            @Override
            public int compare(Users o1, Users o2) {
    
                return o1.getName()-o2.getName();
            }
        });

使用lambda表达式再简化

TreeSet<Users> U=new TreeSet<Users>((o1,o2)->{
    
            return o1.getName()-o2.getName();
            } );

Comparator和Comparable如何选择？

当比较规则不会发生改变的时候，或者说当比较规则只有1个的时候，建议实现Comparable接口；当比较规则有多个，并且需要多个比较规则之间平凡切换，建议使用Comparator接口。