Comparison problems encountered in recent study

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I met some comparative content when I was doing the title , To make a summary

compareTo Comparison method

The example is ：

Define an interface to compare two objects .
interface CompareObject{
public int compareTo(Object o); // If the return value is 0 , For equality ; If it's a positive number , Represents the size of the current object ; A negative number indicates that the current object is small
}
Define a Circle class , Statement redius attribute , Provide getter and setter Method
Define a ComparableCircle class , Inherit Circle Class and implement CompareObject Interface . stay ComparableCircle The methods in the interface are given in the class compareTo Implementation of , Used to compare the radius of two circles .
Define a test class InterfaceTest, Create two ComparableCircle object , call compareTo Method to compare the radius of two classes .
The code is as follows ：

• Interface CompareObject（ Define a comparison method compareTo）：

package com.object_04.interface_05;

public interface CompareObject {
    
        public int compareTo(Object o);
        // If the return value is  0 ,  For equality ;  If it's a positive number , Represents the size of the current object ; A negative number indicates that the current object is small 
    }

• Define a Circle class

package com.object_04.interface_05;
// Define a Circle class 
public class Circle {
    
    private double redius; // Define a radius 

    public Circle() {
    
    }

    public Circle(double redius) {
    
        this.redius = redius;
    }

    public double getRedius() {
    
        return redius;
    }

    public void setRedius(double redius) {
    
        this.redius = redius;
    }

    public int compareTo(Object o) {
    
        System.out.println(" The radius is ："+redius);
        return 0;
    }
}

• Define a ComparableCircle class
• Rewriting is the top priority for success , Here's an important point , Is to this.getRedius() And ((Circle) o).getRedius() There must be a return value when comparing , The corresponding results can be output when the test class is printed

package com.object_04.interface_05;
// Define a ComparableCircle class , Inherit Circle Class and implement CompareObject Interface .
//  stay ComparableCircle The methods in the interface are given in the class compareTo Implementation of , Used to compare the radius of two circles 
public class ComparableCircle extends Circle implements CompareObject {
    
    public ComparableCircle() {
    
    }

    public ComparableCircle(double redius) {
    
        super(redius);
    }

    @Override   // Rewrite the comparison method 
    public int compareTo(Object o) {
    
        //  Operator prediction 
        if (o instanceof Circle){
    
            // If you don't predict, there will be ClassCastException  Class conversion exception 
//  And then compare them 
          if(this.getRedius() == ((Circle) o).getRedius()){
    
              return 0;
          }else if(this.getRedius() < ((Circle) o).getRedius()){
    
              return -1;
          }else {
    
              return 1;
          }
        }
        return 2;
    }
}

• Test class

```java
 - package com.object_04.interface_05;

public class InterfaceTest {
    
    public static void main(String[] args) {
    
        CompareObject c1 = new ComparableCircle(10);
        //  Polymorphic and native states can be used , Use polymorphism first （ Stand high and look far ）
        CompareObject c2 = new ComparableCircle(20);
        int compRs = c1.compareTo(c2);
        System.out.println(compRs);
        switch (compRs) {
    
            case 0:
                System.out.println(" equal ");
                break;
            case 1:
                System.out.println(" Left large ");
                break;
            case -1:
                System.out.println(" Big on the right ");
                break;

            default:
                break;
        }

    }
}

Another comparison of doing exercises is ：
Write salary system , Realize different types of employees ( polymorphic ) The salary is paid on a monthly basis . If a certain... Occurs in the current month
Employee Object's birthday , The employee's salary will be increased 100 element .
Experimental instructions ：
（1） Define a Employee class , This class contains ：
private Member variables name,number,birthday, among birthday by MyDate Class object ;
abstract Method earnings();
toString() Method outputs the name of the object name,number and birthday.
（2）MyDate Class inclusion :
private Member variables year,month,day ;
toDateString() Method returns the string corresponding to the date ：xxxx year xx month xx Japan
（3） Definition SalariedEmployee Class inheritance Employee class , Employees who are paid on a monthly basis
The reason is . This category includes ：private Member variables monthlySalary;
Abstract methods that implement the parent class earnings(), This method returns monthlySalary value ;toString() Method input
Give the employee type information and employee's information name,number,birthday.
（4） reference SalariedEmployee Class definition HourlyEmployee class , Realize the processing of employees whose wages are calculated by hour . This category includes ：
private Member variables wage and hour;
Abstract methods that implement the parent class earnings(), This method returns wage*hour value ;
toString() Method to output employee type information and employee information name,number,birthday.
（5） Definition PayrollSystem class , establish Employee Variable array and initialize , This array stores references to various employee objects . Use the loop structure to traverse the array elements , Output the type of each object ,name,number,birthday, And the object's birthday . When the current month value is entered on the keyboard , If this month is a Employee Object's birthday , Also output salary increase information .

• establish Employee class （ The employee class ）

 package com.object_04.interface_04;

// establish Employee class 
public abstract class Employee {
    
    // full name 
    private String name;
    // Job number 
    private String num;
    // Birthday 
    private MyDate birthday;

    // Construction method 
    public Employee(String name, String num, MyDate birthday) {
    
        this.name = name;
        this.num = num;
        this.birthday = birthday;
    }

    // No arguments structure   It's OK not to write 
    public Employee() {
    

    }

    // Abstract class methods 
    public abstract double earnings();

    @Override
    public String toString() {
    
        return "name:" + name + ",num:" + num + ",birthday:" + birthday;
    }

    public MyDate getBirthday() {
    
        return birthday;
    }

    public String getName() {
    
        return name;
    }

    public abstract MyDate getBirthdayElement(int i);
}

• Create employee salary category SalariedEmployee

package com.object_04.interface_04;


public class SalariedEmployee extends Employee{
    
    // regular employee   Pay monthly salary 
    private double monthlySalary;

    public SalariedEmployee(){
    
    }

    public SalariedEmployee(String name, String num, MyDate birthday, double monthlySalary){
    
        super(name, num, birthday);
        this.monthlySalary = monthlySalary;
    }


    // Override parent class Employee Of earnings（） Method 
    @Override
    public double earnings() {
    
        return monthlySalary;
    }

    @Override
    public String toString() {
    
        return super.toString() + ", salary ："+this.earnings();
    }

    @Override
    public MyDate getBirthdayElement(int i) {
    
        return null;
    }
}

• Hourly wage HourlyEmployee

package com.object_04.interface_04;

// Hourly work   Pay by hour 
public class HourlyEmployee extends Employee{
    
    // Hourly wage 
    private double wage;
    // Time 
    private double hour;

    public HourlyEmployee(String name, String num, MyDate birthday, double wage, double hour){
    
        //super Inherited parent class 
        super(name, num, birthday);
        this.wage = wage;
        this.hour = hour;
    }

    public HourlyEmployee(String  Tu Anli , int i, com.object_04.interface_04.MyDate myDate, int wage, int hour) {
    
    }

    // Override parent class Employee Of earnings（） Method 
    @Override
    public double earnings() {
    
        return wage * hour;
    }

    @Override
    public String toString() {
    
        return super.toString()+this.earnings();
    }

    @Override
    public MyDate getBirthdayElement(int i) {
    
        return null;
    }
}

• Payroll system

import java.util.Arrays;
// Payroll system 
public class PayrollSystem {
    
    // Create array   Used to store employee information 
    private Employee[] employees;

    public PayrollSystem(){
    
    }

    @Override
    public String toString() {
    
        return  Arrays.toString(employees);
    }
    // There are parametric structures 
    public PayrollSystem(Employee[] employees){
    
        this.employees = employees;
    }

    // Get array 
    public Employee[] getEmployees() {
    
        return employees;
    }
    // Change array 
    public void setEmployees(Employee[] employees) {
    
        this.employees = employees;
    }
}

• Test class

package com.object_04.interface_04;

import java.util.Scanner;

public class EmployeeTest {
    
    public static void main(String[] args) {
    
        // Create a PayrollSystem It's like creating a financial system 
        // Used to store employee information 
        PayrollSystem payrollSystem = new PayrollSystem();
        MyDate e1B = new MyDate(2000,10,1);
        Employee e1 = new SalariedEmployee(" Zhang San ","A001",e1B,5000.0);
        Employee e2 = new SalariedEmployee(" Li Si ","A002",e1B,5000.0);

        // Create array   Give it a value   Give him to payroSystem Array assignment of 
        Employee[] employees = {
    e1,e2};
        // Give him to payrollSystem Array of 
        payrollSystem.setEmployees(employees);
        Scanner scanner = new Scanner(System.in);
        while (true){
    
            System.out.println(" Function list ：" +
                    "1、 List employee information " +
                    "2、 Enter month " +
                    "3、 sign out ");
            System.out.print(" Please enter the command to execute ：");
            int s1 = scanner.nextInt();
            if(s1 == 1){
    
                for (int i = 0;i<employees.length;i++){
    
                    System.out.println(employees[i]);
                }
            }else if(s1 == 3){
    
                return;
            }else if(s1 == 2){
    // Increase staff 
                System.out.print(" Please enter the month ：");
                int s2 = scanner.nextInt();
                for(int i = 0;i < payrollSystem.getEmployees().length;i++){
    
                    System.out.println(employees[i]);
                    System.out.println(employees[i].getBirthday());
                    System.out.println(employees[i].getBirthday().getMonth());
                    if(employees[i].getBirthday().getMonth()==(s2)){
    
                        System.out.println(employees[i].getName()+" Birthday of the month , Reward 100 element ");
                    }else{
    
                        continue;
                    }
                }
            }
        }
    }
 }

equals() Method

String class equals() Method is used to compare whether the contents of two strings are equal .

grammar

public boolean equals(Object anObject)

Parameters
Return value
If the given object is equal to a string , Then return to true; Otherwise return to false.

public class Test {
    
    public static void main(String args[]) {
    
        String Str1 = new String("runoob");
        String Str2 = Str1;
        String Str3 = new String("runoob");
        boolean retVal;

        retVal = Str1.equals( Str2 );
        System.out.println(" Return value  = " + retVal );

        retVal = Str1.equals( Str3 );
        System.out.println(" Return value  = " + retVal );
    }
}

The execution result of the above procedure is ：

Return value = true
Return value = true
Details visible ：Java String equals() Method | Novice tutorial (runoob.com)

About java More common comparison methods in (88 Bar message ) Java The comparison method of _m0_67351863 The blog of -CSDN Blog _java Compare

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