JAVA的知识储备升级
Day1 面向对象之多态
1.0 多态的格式
2.0多态中成员变量的使用特点
public class FU {
int num=10;
public void meth()
{
System.out.println(num);
}
}
public class ZI extends FU{ int num=20; @Override public void meth() { System.out.println(num); } }
public class Main {
public static void main(String[] args) {
FU fu=new ZI();
System.out.println(fu.num); //10;
fu.meth();//20
}
}
3.0 多态中成员方法的使用特点
public class FU {
public void meth1()
{
System.out.println("AAA");
}
public void methfu()
{
System.out.println("父类特有方法！");
}
}
public class ZI extends FU{
public void methzi()
{
System.out.println("子类特有方法！" );
}
}
public class Main {
public static void main(String[] args) {
FU fu=new ZI();
//fu.methzi() 编译看左边 父类没有methzi()
fu.methfu();// 执行看右边 没有则向上找
fu.meth1();
}
}
4.0 对象的向上和向下转型
public abstract class Animals {
public abstract void eat();
}
public class Cat extends Animals {
@Override
public void eat() {
System.out.println("猫吃鱼");
}
public void catchmouse()
{
System.out.println("猫捉老鼠");
}
}
public class Main {
public static void main(String[] args) {
Animals animal=new Cat();
animal.eat();
//animal.catchmouse();//编译看左边 父类无此方法
//向下转型
Cat cat=(Cat)animal;
cat.catchmouse();
}
}
打印结果：
猫吃鱼
猫捉老鼠
5.0 笔记本USB接口案例 实现
public interface USB {
public abstract void opendevice();
public abstract void offdevice();
}
public class Computer {
public void open()
{
System.out.println("电脑开机");
}
public void off()
{
System.out.println("电脑关机");
}
public void opendevices(USB usb)
{
usb.opendevice();
if(usb instanceof Keyboard)
{
Keyboard keyboard=(Keyboard)usb;
keyboard.type();
}
else if(usb instanceof Mouse)
{
Mouse mouse=(Mouse) usb;
((Mouse) usb).click();
}
usb.offdevice();
}
}
public class Keyboard implements USB{
@Override
public void opendevice() {
System.out.println("打开键盘");
}
@Override
public void offdevice() {
System.out.println("关闭键盘");
}
public void type()
{
System.out.println("键盘输入");
}
}
public class Mouse implements USB{
@Override
public void opendevice() {
System.out.println("打开鼠标");
}
@Override
public void offdevice() {
System.out.println("关闭鼠标");
}
public void click()
{
System.out.println("鼠标点击");
}
}
public class Main {
public static void main(String[] args) {
Computer com=new Computer();
com.open();
//准备一个鼠标，供电脑使用
//Mouse mouse=new Mouse();
//USB usb=mouse;//向上转型
USB usb=new Mouse();//多态做法
com.opendevices(usb);
Keyboard keyboard=new Keyboard();//没使用向上转型 这里可以理解为自动转型 由小范围到大范围
com.opendevices(keyboard);
//com.opendevices(new Keyboard())
com.off();
}
}
打印结果：
电脑开机
打开鼠标
鼠标点击
关闭鼠标
打开键盘
键盘输入
关闭键盘
电脑关机
Day2 final关键字
1.0 final关键字概念与四种用法
2.0 final修饰一个类
3.0 final修饰一个局部变量
public class People {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public People(String name) {
this.name = name;
}
public People()
{}
}
public class FinalMain {
public static void main(String[] args) {
int num1=10;
System.out.println(num1);
num1=20;
System.out.println(num1);
final int num2=30;
//num2=40
//num2=30
System.out.println(num2);
final int num3;
num3=40 ;//正确方法！
System.out.println(num3);
People people1=new People("金泰亨");
System.out.println(people1);//地址
people1=new People("田柾国");
System.out.println(people1);
people1.setName("朴智旻");//内容可以改变 对引用类型来说不可改变的是地址
}
}
打印结果：
10
20
30
40
People@50cbc42f
People@75412c2f
4.0 final修饰成员变量
public class Finaldemo {
private final String name;
//通过构造方法赋值
public Finaldemo() {
name="徐穗珍";
}
public Finaldemo(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
Day3 内部类
1.0 内部类的概念、分类以及定义
2.0 内部类的使用
public class Outer {//间接方式
class Inner{
public void methodinner()
{
System.out.println("内部方法执行！");
}
}
public void methodouter()
{
System.out.println("外部方法执行！");
new Inner().methodinner();
}
}
public class Main {
public static void main(String[] args) {
Outer outer=new Outer();
outer.methodouter();
}
}
直接方式
public class Outer {
class Inner{
public void methodinner()
{
System.out.println("内部方法执行！");
}
}
public void methodouter()
{
System.out.println("外部方法执行！");
}
}
public class Main {
public static void main(String[] args) {
Outer.Inner inner=new Outer().new Inner();
inner.methodinner();
}
}
打印结果：
内部方法执行！
3.0 内部类的同名变量的访问
public class Outer {
int num=10;
class Inner {
int num=20;
public void method()
{
int num=30;
System.out.println(num);//30
System.out.println(this.num);//20
System.out.println(Outer.this.num);//10
}
}
}
4.0 局部内部类的定义
public class Outer {
public void methodOuter()
{
class Inner
{
int num=10;
public void metehod()
{
System.out.println(num);
}
}
Inner inner=new Inner();
inner.metehod();
}
}
public class Main {
public static void main(String[] args) {
Outer outer=new Outer();
outer.methodOuter();
}
}
打印结果：
10
5.0 局部内部类的final问题
6.0 匿名内部类
1）使用
public interface Interface {
public abstract void method();
}
public class Main {
public static void main(String[] args) {
Interface impl=new Interface() {
@Override
public void method() {
System.out.println("接口覆盖重写方法执行");
}
};
impl.method();
}
}
打印结果：
接口覆盖重写方法执行
2）注意事项
7.0 类作为成员变量
public class Weapon {
private String device;
public Weapon() {
}
public Weapon(String device) {
this.device = device;
}
public String getDevice() {
return device;
}
public void setDevice(String device) {
this.device = device;
}
}
public class Hero {
private String name;
private int age;
private Weapon weapon;
public Hero() {
}
public Hero(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 Weapon getWeapon() {
return weapon;
}
public void setWeapon(Weapon weapon) {
this.weapon = weapon;
}
public void crack()
{
System.out.println(getAge()+" "+getName()+" 使出了"+weapon.getDevice());
}
}
public class Main {
public static void main(String[] args) {
Hero hero=new Hero("妲己",18);
Weapon weapon=new Weapon();
weapon.setDevice("放大招");
hero.setWeapon(weapon);
hero.crack();
}
}
打印结果：
18 妲己 使出了放大招
8.0 使用接口作为成员变量
public interface Skill {
public abstract void device();
}
public class Interfaced implements Skill{
@Override
public void device() {
System.out.println("背水一战");
}
}
public class Hero {
private int age;
private String name;
private Skill skill;
public Hero() {
}
public Hero(int age, String name, Skill skill) {
this.age = age;
this.name = name;
this.skill = skill;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Skill getSkill() {
return skill;
}
public void setSkill(Skill skill) {
this.skill = skill;
}
public void crack()
{
System.out.print("我是"+getAge()+"岁的"+getName()+"正在放出技能");
skill.device();
}
}
public class Main {
public static void main(String[] args) {
Interfaced impl=new Interfaced();
Hero hero=new Hero();
hero.setName("韩信");
hero.setAge(18);
/*
*第一种创建Skill接口的实现类
* hero.setSkill(impl);
* hero.crack();
* 我是18岁的韩信正在放出技能背水一战
* */
/*
* 第二种使用匿名内部类
* Skill skill=new Skill() {
@Override
public void device() {
System.out.println("背水一战");
}
};
* hero.setSkill(skill);
* hero.crack();//我是18岁的韩信正在放出技能背水一战
* */
/*第三种使用匿名对象 匿名内部类*/
hero.setSkill(new Skill() {
@Override
public void device() {
System.out.println("背水一战");
}
});
hero.crack();//我是18岁的韩信正在放出技能背水一战
}
}