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