Comparator (interface between comparable and comparator)

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Concept

The comparator ： Compare two or more data , To determine whether they are equal , Or determine the size relationship and order between them ( From Baidu ).

Java The comparator in is mainly through Realization Comparable And Comparator Two interfaces To achieve

Comparable Interface

Inherit interfaces through classes , In a class CompareTo() Method to copy and complete the comparison

The main implementation statements ：

class +implements Comparable<>{

…

public int compareTo(Work o){

return 0;

}

}

Comparison method ：

adopt if(){}else{} Statement to determine the return value is -1,1,0 Which of them , When used, you return -1,1,0 To arrange the comparators in order .

Comparable Attention to interface implementation ： The implementation location of the interface should be in the location of the class , Such as Worker Class so Comparable The interface should be in Worker In the class implementation .

for example ：

 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  {
       // If the first condition is equal , The second condition of comparison 
            if (this.age > o.age) {
    
                return 1;
            } else if (this.age < o.age) {
    
                return -1;
            } else{
    
                return 0;
            }

        }
 }

Comparable Interface instance ：

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(" Zhang San ",30,9000));
        list.add(new Worker(" Li Si ",31,12000));
        list.add(new Worker(" Wang Wu ",28,9000));
        list.add(new Worker(" The king of the three ",23,9000));
        list.add(new Worker(" The king 2 ",26,12000));
        list.add(new Worker(" Wang Liu ",30,12000));
        list.add(new Worker(" Li Meili ",48,12000));
        list.add(1,new Worker(" Zhao Liu ",26,3300));

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

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

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


       Collections.sort(list);  //ComparableTo
        // use sort Methods the sorting , The sorting condition is written in ComparaTo Conditions in 
        
        System.out.println(" After ordering ");
        Iterator<Worker> it1=list.iterator();
        while(it1.hasNext()){
    
            Worker s=it1.next();
            System.out.println(s);
        }
    }
}

 Execution results :

Worker{name=' Zhang San ', age=30, salary=9000.0}
Worker{name=' Zhao Liu ', age=26, salary=3300.0}
Worker{name=' Li Si ', age=31, salary=12000.0}
Worker{name=' The king of the three ', age=23, salary=9000.0}
Worker{name=' The king 2 ', age=26, salary=12000.0}
Worker{name=' Wang Liu ', age=30, salary=12000.0}
Worker{name=' Li Meili ', age=48, salary=12000.0}
 After ordering 
Worker{name=' The king 2 ', age=26, salary=12000.0}
Worker{name=' Wang Liu ', age=30, salary=12000.0}
Worker{name=' Li Si ', age=31, salary=12000.0}
Worker{name=' Li Meili ', age=48, salary=12000.0}
Worker{name=' The king of the three ', age=23, salary=9000.0}
Worker{name=' Zhang San ', age=30, salary=9000.0}
Worker{name=' Zhao Liu ', age=26, salary=3300.0}

Comparator( The comparator ) Interface

The main implementation statements ：

class +implements Comparator<>{

…

public int compare(Worker o1,Worker o2){

return 0;

}

}

Comparison method ：

adopt if(){}else{} Statement to determine the return value is -1,1,0 Which of them , When used, you return -1,1,0 To arrange the comparators in order .

Comparator Attention to interface implementation ： The implementation position of the interface should Not in the location of the class , Such as Worker Class so Comparable Interface cannot be in Worker In the class implementation .

Comparator The design of the interface complies with OCP principle .

for example ：

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 Interface instance

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(" Zhang San ",30,9000));
        list.add(new Worker(" Li Si ",31,12000));
        list.add(new Worker(" Wang Wu ",28,9000));
        list.add(new Worker(" The king of the three ",23,9000));
        list.add(new Worker(" The king 2 ",26,12000));
        list.add(new Worker(" Wang Liu ",30,12000));
        list.add(new Worker(" Li Meili ",48,12000));
        list.add(1,new Worker(" Zhao Liu ",26,3300));

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

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

 Execution results ：

Worker{name=' Zhang San ', age=30, salary=9000.0}
Worker{name=' Zhao Liu ', age=26, salary=3300.0}
Worker{name=' Li Si ', age=31, salary=12000.0}
Worker{name=' The king of the three ', age=23, salary=9000.0}
Worker{name=' The king 2 ', age=26, salary=12000.0}
Worker{name=' Wang Liu ', age=30, salary=12000.0}
Worker{name=' Li Meili ', age=48, salary=12000.0}
 After ordering 
Worker{name=' The king 2 ', age=26, salary=12000.0}
Worker{name=' Wang Liu ', age=30, salary=12000.0}
Worker{name=' Li Si ', age=31, salary=12000.0}
Worker{name=' Li Meili ', age=48, salary=12000.0}
Worker{name=' The king of the three ', age=23, salary=9000.0}
Worker{name=' Zhang San ', age=30, salary=9000.0}
Worker{name=' Zhao Liu ', age=26, salary=3300.0}

Anonymous inner class pairs can also be used Comparator and Comparable Interface simplification

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

Use lambda Expression re simplification

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

Comparator and Comparable How to choose ？

When the rules of comparison don't change , Or when the rules of comparison are only 1 When it's time , It is suggested that Comparable Interface ; When there are more than one comparison rule , And it requires ordinary switching between multiple comparison rules , It is recommended to use Comparator Interface .