黑马程序员学习笔记

接口interface

接口中：变量默认为常量，方法默认为抽象方法

• 接口不能创建对象；
• 一个累可以实现多个接口，但是只能继承（extends）一个父类
• 实现多个接口要重写全部接口的全部抽象方法，否则定义该实现类为抽象类
• 实现接口用关键字implements。alt+回车重写接口所有方法

好处

• 弥补了单类继承的不足，一个类可以同时实现多个接口
  - 让程序可以面向接口编程，这样就可以灵活的切换各种业务的实现
  

为什么要用接口

看到接口，别人显性地知道你是谁，有什么功能，从而放心地使用

接口案例

需求

思路

代码

Student.java

/**
 * @Author: ggdpzhk
 * @CreateTime: 2024-08-13
 */
public class Student {
    private String name;
    private String sex;
    private double grade;


    public double getGrade() {
        return grade;
    }

    public void setGrade(double grade) {
        this.grade = grade;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Student(String name, String sex, double grade) {
        this.name = name;
        this.sex = sex;
        this.grade = grade;
    }
    public Student() {
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", grade=" + grade +
                '}';
    }
}

ClassManage.java

import java.util.ArrayList;

/**
 * @Author: ggdpzhk
 * @CreateTime: 2024-08-13
 */
public  class ClassManage{
    private ArrayList<Student> students = new ArrayList<>();
    private StudentOperator studentOperator = new StudentOperatorImpl1();
    //private StudentOperator studentOperator = new StudentOperatorImpl2();

    public ClassManage() {
        students.add(new Student("张三", "男", 90));
        students.add(new Student("李四", "女", 80));
        students.add(new Student("王五", "男", 70));
        students.add(new Student("赵六", "女", 60));
    }

    public void printStudent() {
        studentOperator.printAllStudent(students);
    }
    public void printGrade() {
        studentOperator.printAverageGrade(students);
    }
}

• 切换方案只需要修改
  

StudentOperator 接口

import java.util.ArrayList;

public interface StudentOperator {
    void printAllStudent(ArrayList<Student> students);
    void printAverageGrade(ArrayList<Student> students);
}

StudentOperatorImpl1.java

import java.util.ArrayList;

public class StudentOperatorImpl1 implements StudentOperator {


    @Override
    public void printAllStudent(ArrayList<Student> students) {
        for (Student i : students){
            System.out.println(i.toString());
        }
    }

    @Override
    public void printAverageGrade(ArrayList<Student> students) {
        double sum = 0;
        for (Student i : students){
            sum += i.getGrade();
        }
        System.out.println("平均成绩为：" + sum / students.size());
    }
}

StudentOperatorImpl2.java

import java.util.ArrayList;

public class StudentOperatorImpl2 implements StudentOperator {


    @Override
    public void printAllStudent(ArrayList<Student> students) {
        int girl = 0;
        for (Student i : students) {
            if (i.getSex().equals("女")) {
                girl++;
                System.out.println(i.toString());
            }
        }
        System.out.println("女生数量：" + girl);
        System.out.println("男生数量：" + (students.size() - girl));
    }

    @Override
    public void printAverageGrade(ArrayList<Student> students) {
        int sum = 0;
        double grades = 0;
        double max = students.get(0).getGrade();
        double min = students.get(0).getGrade();
        for (int i = 0; i < students.size(); i++) {
            if (students.get(i).getGrade() <= max) {
                sum++;
                grades += students.get(i).getGrade();
                min = students.get(i).getGrade();
            }
            if (students.get(i).getGrade() > min) {
                sum++;
                grades += students.get(i).getGrade();
                max = students.get(i).getGrade();
            }
        }
        System.out.println("平均分：" + (grades - max - min) / (sum - 2));
    }
}

Test.java

/**
 * @Author: ggdpzhk
 * @CreateTime: 2024-08-13
 */
public class Test {
    public static void main(String[] args) {
        ClassManage classManage = new ClassManage();
        classManage.printGrade();
        classManage.printStudent();
    }
}