[Java知识库]Java类对象（笔记）持续完善中……

一些范例

0.0

public class qwer{
	public static void main(String[] args){
		Person p1 = new Person();
		}
	}
} 


class Person{
}


class Person{
	public Person{
	}
}


class Person{
	int age;
	public Person(int a){
	}
}

基础

1.0

public class qwer {
    public static void main(String[] args) {
        Person p2 = new Person();
        Person p1 = new Person();
        p1.setAge(30);
        p1.setName("Zhangsan");
        p2.setAge(-80);
        p2.setName("lisi");
        p1.introudce();
        p2.introudce();
    }
}
class Person{
    private int age;
    private String name;

    public String getName(){                  //获取值
        return name;
    }
    public void setName(String perName) {     //设置值
        name = perName;
    }

    public int getAge(int perAge) {
        return age;
    }

    public void setAge(int perAge) {
        if(perAge<0)
            System.out.println("null");
        else
            age=perAge;
    }
    public void introudce(){
        System.out.println("I am "+name+".");
        System.out.println("I am "+age+"years old.");
    }
}

1.1

 public class qwer {
    public static void main(String[] args) {
        Person p2 = new Person(55);
        p2.speak();
    }
}
class Person{
    int age;
    public Person(int a){
        age=a;
    }
    public void speak(){
        System.out.println("I am "+age+" years old.");
    }
}

1.2

public class qwer {
    public static void main(String[] args) {
        Person p1 = new Person("张三",18);
        Person p2 = new Person("王五");
        p1.speak();
        p2.speak();
    }
}
class Person{
    String name;
    int age;
    public Person(String con_name,int con_age){     //定义两个参数的构造方法
        name=con_name;                              //为name属性赋值
        age=con_age;
    }
    public Person(String con_name){                 //为Person p2 = new Person("王五");服务，不然无法输出0岁的结果
        name=con_name;
    }
    public void speak(){
        System.out.println("我是"+name+"，我今年"+age+"岁。");
    }
}

1.3

public class qwer {
    public static void main(String[] args) {
        Person p = new Person("qqqqqqqqq");
    }
}
class Person{
    public Person(){
        System.out.println("aaaaaaaaa");
    }
    public Person(String name){
        this();     //无this有q则输出b   有this有q则输出a \n b   有（无）this无q则输出a   
        System.out.println("bbbbbbbbb");
    }
}

1.4 静态内部类

public class qwer {
    public static void main(String[] args) {
        Person.Inner inner = new Person.Inner();       //创建内部类对象
        inner.show();
    }
}
class Person{
    private static int num=6;
    static class Inner{                                //定义内部类
        void show(){
            System.out.println("num="+num);
        }
    }
}

1.5 方法内部类

public class qwer {
    public static void main(String[] args){
        Outer outer = new Outer();
        outer.test();
    }
}
class Outer{
    private int a=4;
    public  void test(){
        class Inner{                       //方法中定义内部类
            void show(){
                System.out.println(a);
            }
        }
        Inner in = new Inner();           //创建内部类对象
        in.show();                        //调用内部类对象
    }
}

继承

2.1 继承

public class qwer {
    public static void main(String[] args){
        Dog dog = new Dog();
        dog.name="沙皮狗";
        dog.printName();
        dog.shout();

    }
}
class Animal{
    String name;
    void shout(){
        System.out.println("汪汪汪");
    }
}
class Dog extends Animal{
    public void printName(){
        System.out.println(name);
    }
}

2.2 类的继承

public class qwer {
    public static void main(String[] args){
        Dog dog = new Dog();
        dog.name="沙皮狗";
        dog.printName();
        dog.shout();

    }
}
class Animal{
    String name;
    void shout(){
        System.out.println("汪汪汪");
    }
}
class Dog extends Animal{             //dog类继承animal类（关键字：extends）
    public void printName(){          
        System.out.println(name);
    }
}

2.3 多个子类可以继承于一个父类

public class qwer {
    public static void main(String[] args){
        Dog dog = new Dog();
        Cat cat = new Cat();
        dog.shout();                //调动Dog类继承来的shout()方法
        dog.name="沙皮狗";
        dog.dogName();
        dog.dogMove();
        cat.shout();
        cat.catName();
        cat.catMove();
    }
}
class Animal{
    String name;
    void shout(){
        System.out.println("有一只");
    }
}
class Dog extends Animal{             //dog类继承animal类（关键字：extends）
    public void dogName(){
        System.out.println(name);
    }
    public void dogMove(){
        System.out.println("快快的跑");
    }
}
class Cat extends Animal{
    public void catName(){
        System.out.println("加菲猫");
    }
    public void catMove(){
        System.out.println("蹬蹬的跑");
    }
}

2.4 super关键字

public class qwer {
    public static void main(String[] args){
        Dog dog = new Dog();
        dog.shout();
        dog.printNmae();
    }
}
class Animal{
    String name="动物";
    void shout(){
        System.out.println("你是一只");
    }
}
class Dog extends Animal{
    String name="沙皮狗";
    void shout() {
        super.shout();
    }
    void printNmae(){
        System.out.println(super.name);     //super.name直接调用的是父类的，不调用子类中的name=沙皮狗
    }
}

2.5 final 关键字

public class qwer {
    public static void main(String[] args){
        final int a=6;             //final只能定义常量，只能一次赋值
        a=10;                       //再次赋值报错
}

抽象、接口

3.1 抽象类

public class qwer {
    public static void main(String[] args){
        Dog dog = new Dog();
        dog.shout();
    }
}
abstract class Animal{
    abstract void shout();
}
class Dog extends Animal{
    void shout(){
        System.out.println("汪汪汪……");
    }
}

3.2 接口

public class qwer {
    public static void main(String[] args){
        Dog dog = new Dog();
        dog.breathe();
        dog.run();
    }
}
interface Animal{
		int ID=1;
    void breathe();
    void run();
}
class Dog implements Animal{            //Dog类实现了Animal接口
    public void breathe(){
        System.out.println("狗崽在呼吸");
    }
    public void run(){
        System.out.println("狗崽在狂奔");
    }
}

3.3 接口继承

public class qwer {
    public static void main(String[] args){
        Dog dog = new Dog();
        dog.Move();
        dog.breathe();
        dog.run();
    }
}
interface Animal{                         //定义接口
    int ID=1;
    void breathe();
    void run();
}
interface Quanke extends Animal{          //接口继承上一个接口
    void Move();
}
class Dog implements Quanke{             //类实现接口
    public void breathe(){
        System.out.println("狗崽在呼吸");
    }
    public void run(){
        System.out.println("狗崽在狂奔");
    }
    public void Move() {
        System.out.println("狗崽活着");
    }
}

3.4 多态

public class qwer {
    public static void main(String[] args){
        Animal an1 = new Cat();
        Animal an2 = new Dog();
        Animalshout(an1);                              //an1作为参数，调用Animalshout方法
        Animalshout(an2);
    }
    public static void Animalshout(Animal an){         //定义Animalshout方法：再调用shout方法
        an.shout();
    }
}
interface Animal{                          
    void shout();
}
class Cat implements Animal{
    public void shout(){
        System.out.println("喵喵……");
    }
}
class Dog implements Animal{
    public void shout(){
        System.out.println("汪汪……");
    }
}