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【详细+超基础】Java-学习笔记 06
发布日期：2021-04-30 21:12:16 浏览次数：91 分类：精选文章

本文共 9310 字，大约阅读时间需要 31 分钟。

Java??????????

???Java???????????????????????????????????????????????????????????????????????????????????????????????????????????????????Java???????

???????

1.1 ?????

??????????????????????????????????????????????????????????????????????????????????????????????????

1.2 ???????

?Java??????extends??????????????

class ?? extends ?? {
    // ?????
}

?????

public class Fu {   // ??
    public void show() {   // ????
        System.out.println("show?????");
    }
}
public class Zi extends Fu {   // ??
    public void method() {   // ????????
        System.out.println("method?????");
    }
}
public class Demo {   // ???
    public static void main(String[] args) {
        Fu f = new Fu();   // ??????
        f.show();   // ??????
        Zi z = new Zi();   // ??????
        z.method();   // ??????
        z.show();   // ???????????
    }
}

1.3 ????????

?????

  • ???????????????????????????????????
  • ????????????????????????????????????????

    • ?????

  • ??????????????????????????????????????????
  • ?????????????????????????????????

    • 1.4 ???????

    ???????????????????????????????????

    • is-a??????Student?Teacher???Person????Person???????
    • has-a????????Car??????Engine???Car??????Vehicle?????

    ????????????

    ?Java???????????????????????????

    2.1 ??????????

    ??????????????????????

  • ??????????????????
  • ??????????????????????
  • ????????????????????????
  • ???????????

    • ?????

    class Fu {   // ??
        int num = 10;   // ????
    }
    class Zi {   // ??
        int num = 20;   // ????
        public void show() {
            int num = 30;   // ??????
            System.out.println(num);   // ??30
        }
    }
    public class Demo1 {
        public static void main(String[] args) {
            Zi z = new Zi();
            z.show();   // ????????30
        }
    }

    2.2 super???

    super?this????????????????

    • super??????????????????????????
    • this??????????????????????????

    super?????

  • ?????
    • this.???????????????
    • super.???????????????
  • ?????
    • this.???????????????
    • super.???????????????
  • ?????
    • this(??)???????????
    • super(??)???????????

    • ?????

    public class Fu {
        public void show() {
            System.out.println("Fu?show()?????");
        }
    }
    public class Zi extends Fu {
        @Override
        public void show() {
            System.out.println("Zi?show()?????");
            super.show();   // ?????show??
        }
    }
    public class Demo {
        public static void main(String[] args) {
            Zi z = new Zi();
            z.show();   // ??Zi?show()?????
        }
    }

    2.3 ????????????

    ?????????????????????????????????????????????super()????????????????????????????????

    ?????

    public class Fu {
        public Fu() {
            System.out.println("Fu???????");
        }
        public Fu(String name, int age) {
            System.out.println("Fu???????");
        }
    }
    public class Zi extends Fu {
        public Zi() {
            super(10, 20);   // ?????????????
            System.out.println("Zi?????");
        }
    }
    public class Demo {
        public static void main(String[] args) {
            Zi z = new Zi();
            System.out.println("Zi?????");
        }
    }

    2.4 ????????????

    ???????????????????????

  • ??????????????????
  • ??????????????????????
  • ???????????

    • ?????

    public class Fu {
        private void show() {
            System.out.println("Fu?show()?????");
        }
    }
    public class Zi extends Fu {
        @Override
        public void show() {
            System.out.println("Zi?show()?????");
        }
    }
    public class Demo {
        public static void main(String[] args) {
            Zi z = new Zi();
            z.show();   // ??Zi?show()?????
        }
    }

    2.5 ????

    ???????

    ????????????????????????????????????????????????????????????????

    ?????????

    • ??????????????
    • ??????????????????????????

    ???@Override???

    ?Java??@Override???????????????????????????@Override??????

  • ?????????????????
  • ??????????????

    • ?????

    public class Fu {
        public void show() {
            System.out.println("Fu?show()?????");
        }
    }
    public class Zi extends Fu {
        @Override
        public void show() {
            System.out.println("Zi?show()?????");
        }
    }
    public class Demo {
        public static void main(String[] args) {
            Zi z = new Zi();
            z.show();   // ??Zi?show()?????
        }
    }

    ?????????

    3.1 Java?????

    Java?????????????????

    class A extends B, C {   // ???Java??????
    }

    3.2 ????

    Java??????????

    public class Granddad {   // ???
        public void drink() {
            System.out.println("?????");
        }
    }
    public class Father extends Granddad {   // ??????????
        public void smoke() {
            System.out.println("?????");
        }
    }
    public class Mother {   // ???
        public void dance() {
            System.out.println("?????");
        }
    }
    public class Son extends Father {   // ??????????
        // ?????????drink()?smoke()??
    }

    3.3 final??

    final??????????????????????

  • ???????????????????
  • ???????????????
  • ?????????????????????

    • ?????

    public final class Person {   // ?????
        private String name;
        private int age;
        public Person(String name, int age) {
            this.name = name;
            this.age = age;
        }
        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 class Student extends Person {   // ?????Person?
        public Student(String name, int age) {
            super(name, age);
        }
        public void study() {
            System.out.println("?????");
        }
    }

    3.4 static??

    static????????????????????????????????

    ?????

    public class Student {
        public static String university;   // ????
        private String name;
        private int age;
        public Student(String name, int age) {
            this.name = name;
            this.age = age;
        }
        public void show() {
            System.out.println(name + "," + age + "," + university);
        }
    }
    public class Demo {
        public static void main(String[] args) {
            Student.university = "??????";
            Student s1 = new Student("???", 18);
            s1.show();
            Student s2 = new Student("??", 17);
            s2.show();
        }
    }

    3.5 static????

    static????????????????????

  • ????????????static????????
  • ???????????static????????

    • ?????

    public class Student {
        public static String university;   // ????
        private String name;
        private int age;
        public Student(String name, int age) {
            this.name = name;
            this.age = age;
        }
        public void show() {
            System.out.println(name + "," + age + "," + university);
        }
    }
    public class Demo {
        public static void main(String[] args) {
            Student.university = "??????";
            Student s1 = new Student("???", 18);
            s1.show();
            Student s2 = new Student("??", 17);
            s2.show();
        }
    }

    ??????

    4.1 ?????

    ?????

  • ??Teacher??Student?????????????????
  • ???????????????????
  • ??????????????????

    • ?????

  • ??Person???????? 
    class Person {
        private String name;
        private int age;
        public Person(String name, int age) {
            this.name = name;
            this.age = age;
        }
        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;
        }
    }
  • ??Teacher?? 
    class Teacher extends Person {
        public Teacher(String name, int age) {
            super(name, age);
        }
        public void teach() {
            System.out.println("?????");
        }
    }
  • ??Student?? 
    class Student extends Person {
        public Student(String name, int age) {
            super(name, age);
        }
        public void study() {
            System.out.println("?????");
        }
    }
  • ????? 
    public class PersonDemo {
        public static void main(String[] args) {
            // ????????????
            Teacher t1 = new Teacher("???", 18);
            t1.setName("???");   // ????
            t1.setAge(18);   // ????
            System.out.println(t1.getName() + "," + t1.getAge());
            t1.teach();   // ???????
            // ????????????
            Student s = new Student("??", 17);
            System.out.println(s.getName() + "," + s.getAge());
            s.study();   // ???????
        }
    }

    • 4.2 ???

    ?????

  • ??Cat??Dog?????????????????
  • ???????Animal??
  • ????Cat?Dog???Animal??????????

    • ?????

  • ??Animal???????? 
    class Animal {
        private String name;
        private int age;
        public Animal(String name, int age) {
            this.name = name;
            this.age = age;
        }
        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;
        }
    }
  • ??Cat?? 
    class Cat extends Animal {
        public Cat(String name, int age) {
            super(name, age);
        }
        public void catchMouse() {
            System.out.println("????");
        }
    }
  • ??Dog?? 
    class Dog extends Animal {
        public Dog(String name, int age) {
            super(name, age);
        }
        public void lookDoor() {
            System.out.println("???");
        }
    }
  • ????? 
    public class AnimalDemo {
        public static void main(String[] args) {
            // ???????????
            Cat c1 = new Cat();
            c1.setName("?");
            c1.setAge(5);
            System.out.println(c1.getName() + "," + c1.getAge());
            c1.catchMouse();
            // ???????????
            Dog d1 = new Dog("?", 6);
            System.out.println(d1.getName() + "," + d1.getAge());
            d1.lookDoor();
        }
    }

    • ????

    ????????????Java??????????????????????????????????????????????????????????????????????????????????????????????Java?????????????????????????????

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