目录

  • ​​面向对象之三大特性之三：多态​​
  • ​​多态的概述、多态的形式​​
  • ​​多态的好处​​
  • ​​多态下引用数据类型的类型转换​​
  • ​​多态的综合案例​​
  • ​​内部类​​
  • ​​内部类概述​​
  • ​​内部类之一：静态内部类​​
  • ​​内部类之二：成员内部类​​
  • ​​内部类之三：局部内部类​​
  • ​​内部类之四：匿名内部类概述[重点]​​
  • ​​匿名内部类常见使用形式​​
  • ​​匿名内部类真实使用场景演示​​
  • ​​常用API​​
  • ​​Object​​
  • ​​toString方法​​
  • ​​equals方法​​
  • ​​Objects​​
  • ​​StringBuilder​​
  • ​​Math​​
  • ​​System​​
  • ​​BigDecimal​​

面向对象之三大特性之三：多态

多态的概述、多态的形式

Java面向对象之多态、内部类、常用API_System

多态的好处

Java面向对象之多态、内部类、常用API_android_02

多态下引用数据类型的类型转换

Java面向对象之多态、内部类、常用API_开发语言_03


Java面向对象之多态、内部类、常用API_内部类_04

多态的综合案例

Java面向对象之多态、内部类、常用API_开发语言_05

package com.zixin.d4_polymorphic_test;

public interface USB {

    void connect();
    void unconnect();
}
package com.zixin.d4_polymorphic_test;

public class KeyBoard implements USB{
    public String name;

    public KeyBoard(String name) {
        this.name = name;
    }



    @Override
    public void connect() {
        System.out.println(name + "成功连接了电脑~");
    }

    @Override
    public void unconnect() {
        System.out.println(name + "成功从电脑中拔出了~");
    }

    public void keyDown(){
        System.out.println(name+"敲击了：来了，老弟，666，没毛病");
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}
package com.zixin.d4_polymorphic_test;

public class Mouse implements USB{

    private String name;

    public Mouse(String name) {
        this.name = name;
    }

    @Override
    public void connect() {
        System.out.println(name + "成功连接了电脑~");
    }

    @Override
    public void unconnect() {
        System.out.println(name + "成功从电脑中拔出了~");
    }

    public void dbClick(){
        System.out.println(name+"双击点亮小红心，一键三连~~");
    }
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}
package com.zixin.d4_polymorphic_test;

public class Computer {
    private String name;

    public Computer(String name) {
        this.name = name;
    }

    public void start(){
        System.out.println(name + "开机了~~");
    }

    public void installUSB(USB usb){
        usb.connect();

        if(usb instanceof KeyBoard){
            KeyBoard k = (KeyBoard) usb;
            k.keyDown();
        }else if(usb instanceof Mouse){
            Mouse m = (Mouse) usb;
            m.dbClick();
        }

        usb.unconnect();
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}
package com.zixin.d4_polymorphic_test;

public class Test {
    public static void main(String[] args) {
        Computer c =new Computer("外星人");
        c.start();

        USB u =new KeyBoard("燕双飞");
        c.installUSB(u);

        USB u1 = new Mouse("罗技鼠标");
        c.installUSB(u1);
    }
}

内部类

内部类概述

Java面向对象之多态、内部类、常用API_android_06

内部类之一：静态内部类

Java面向对象之多态、内部类、常用API_内部类_07


Java面向对象之多态、内部类、常用API_System_08

package com.zixin.d5_innerclass_static;

public class Outer {
    public static class Inner{
        private String name;
        private int age;
        public static String schoolName;

        public Inner(){}

        public Inner(String name, int age) {
            this.name = name;
            this.age = age;
        }

        public void show(){

        }
        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;
        }

    }
}
package com.zixin.d5_innerclass_static;

public class Test {
    public static void main(String[] args) {
        Outer.Inner in = new Outer.Inner();
        in.setName("张三");
        in.show();
    }
}

Java面向对象之多态、内部类、常用API_内部类_09

内部类之二：成员内部类

内部类之三：局部内部类

内部类之四：匿名内部类概述[重点]

匿名内部类常见使用形式

Java面向对象之多态、内部类、常用API_内部类_10

package com.zixin.d8_innerclass_anonymous;

public class Test {
    public static void main(String[] args) {
        Animal a =new Animal() {
            @Override
            public void run() {
                System.out.println("老虎跑得快~~~");
            }
        };

        a.run();
    }
}

//class Tiger extends Animal{
//    @Override
//    public void run() {
//        System.out.println("老虎跑得快~~");
//    }
//}

abstract class Animal{
    public abstract void run();
}

Java面向对象之多态、内部类、常用API_内部类_11


Java面向对象之多态、内部类、常用API_java_12

package com.zixin.d8_innerclass_anonymous;

public class Test2 {
    public static void main(String[] args) {
        Swimming s =new Swimming() {
            @Override
            public void swim() {
                System.out.println("学生游泳很开心");
            }
        };
        go(s);


        go(new Swimming() {
            @Override
            public void swim() {
                System.out.println("老师游泳很快");
            }
        });
    }

    public static void go(Swimming s){
        System.out.println("开始。。。");
        s.swim();
        System.out.println("结束。。。");
    }
}



interface Swimming{
    void swim();
}

匿名内部类真实使用场景演示

常用API

Object

Java面向对象之多态、内部类、常用API_java_13


Java面向对象之多态、内部类、常用API_开发语言_14

toString方法

Java面向对象之多态、内部类、常用API_android_15

package com.zixin.d9_api_object;

public class Student { // extends Object
    private String name;
    private char sex;
    private int age;

    public Student() {
    }

    public Student(String name, char sex, int age) {
        this.name = name;
        this.sex = sex;
        this.age = age;
    }

    public String getName() {
        return name;
    }

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

    public char getSex() {
        return sex;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", sex=" + sex +
                ", age=" + age +
                '}';
    }
}
package com.zixin.d9_api_object;

public class Test {
    public static void main(String[] args) {
        Student s = new Student("周雄",'男',19);
        System.out.println(s.toString());

        System.out.println(s);

    }
}

Java面向对象之多态、内部类、常用API_android_16

equals方法

Java面向对象之多态、内部类、常用API_内部类_17

package com.zixin.d9_api_object;

import java.util.Objects;

public class Student { // extends Object
    private String name;
    private char sex;
    private int age;

    public Student() {
    }

    public Student(String name, char sex, int age) {
        this.name = name;
        this.sex = sex;
        this.age = age;
    }

    public String getName() {
        return name;
    }

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

    public char getSex() {
        return sex;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return sex == student.sex && age == student.age && Objects.equals(name, student.name);
    }


//    @Override
//    public boolean equals(Object o){
//        if(o instanceof Student){
//            Student s2 = (Student) o;
//
//            return this.name.equals(s2.name) && this.age == s2.age && this.sex==s2.sex;
//        }else{
//            return false;
//        }
//    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", sex=" + sex +
                ", age=" + age +
                '}';
    }
}
package com.zixin.d9_api_object;

public class Test2 {
    public static void main(String[] args) {
        Student s = new Student("周雄",'男',19);
        Student s2 = new Student("周雄",'男',19);
        System.out.println(s.equals(s2));
        System.out.println(s==s2);
    }
}

Java面向对象之多态、内部类、常用API_android_18

Objects

Java面向对象之多态、内部类、常用API_System_19


Java面向对象之多态、内部类、常用API_开发语言_20

StringBuilder

Java面向对象之多态、内部类、常用API_android_21


Java面向对象之多态、内部类、常用API_android_22

package com.zixin.d10_api_objects;

public class StringBuilderDemo1 {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        sb.append("a");
        sb.append(false);
        sb.append(3.3);
        System.out.println(sb);

        StringBuilder sb1 = new StringBuilder();
        sb1.append("a").append("b").append(2);
        System.out.println(sb1);

        sb1.reverse().append(110);
        System.out.println(sb1);

        System.out.println(sb1.length());

        String rs = sb1.toString();
    }
}

Java面向对象之多态、内部类、常用API_开发语言_23


Java面向对象之多态、内部类、常用API_java_24


Java面向对象之多态、内部类、常用API_内部类_25

package com.zixin.d10_api_objects;

public class StringBuilderTest2 {
    public static void main(String[] args) {
        int [] arr1 =null;
        System.out.println(toString(arr1));

        int[] arr2={1,2,3,5};
        System.out.println(toString(arr2));
    }

    public static String toString(int[] arr){
        if(arr !=null){
            StringBuilder sb = new StringBuilder("[");
            for(int i =0;i<arr.length;i++){
                sb.append(arr[i]).append(i== arr.length-1?"":",");
            }
            sb.append("]");
            return sb.toString();
        }
        else{
            return null;
        }
    }
}

Math

Java面向对象之多态、内部类、常用API_System_26

System

Java面向对象之多态、内部类、常用API_开发语言_27


Java面向对象之多态、内部类、常用API_java_28

package com.zixin.d13_system;

import java.sql.Array;
import java.sql.SQLOutput;
import java.util.Arrays;

public class SystemDemo {
    public static void main(String[] args) {
        System.out.println("程序开始。。。");

//        System.exit(0);

        long time = System.currentTimeMillis();
        System.out.println(time);

        long startTime = System.currentTimeMillis();
        for(int i=0;i<100000;i++){
            System.out.println("输出："+i);
        }
        long endTime = System.currentTimeMillis();
        System.out.println(endTime-startTime/1000.0+"s");

        int []arr1 = new int[]{10,20,30,40,50,60,70};
        int [] arr2 = new int[6];
        System.arraycopy(arr1,3,arr2,2,3);
        System.out.println(Arrays.toString(arr2));

        System.out.println("程序结束");
    }
}

BigDecimal

Java面向对象之多态、内部类、常用API_java_29


Java面向对象之多态、内部类、常用API_开发语言_30

package com.zixin.d14_bigdecimal;

import java.math.BigDecimal;

public class BigDecimalDemo {
    public static void main(String[] args) {
        System.out.println(0.09+0.01);

        double a = 0.1;
        double b = 0.2;
        double c = a + b;
        System.out.println(c);
        System.out.println("- ------------");

        BigDecimal a1 = BigDecimal.valueOf(a);
        BigDecimal b1 = BigDecimal.valueOf(b);

        BigDecimal c1 = a1.subtract(b1);
        System.out.println(c1);

        double rs = c1.doubleValue();
        System.out.println(rs);

        System.out.println("--------");

        BigDecimal a11 = BigDecimal.valueOf(10.0);
        BigDecimal b11 = BigDecimal.valueOf(3.0);

        BigDecimal c11 = a11.divide(b11,2,BigDecimal.ROUND_HALF_UP);
        System.out.println(c11);
    }
}

Java面向对象之多态、内部类、常用API_System_31