面向对象

Person

// 描述人类信息
class Person {
    String name; // 姓名
    int age; // 年龄
    static int totalNum = 70; // 表示人的总数
    // 工作
    void work() {
        System.out.println("工作....");
    }
    // 毁灭
    static void destory() {
        System.out.println("毁灭.....");
    }
}

// 演示类/测试类
public class PersonDemo {
    public static void main(String[] args) {
        Person p1 = new Person();
        p1.name = "乔峰";
        p1.age = 32;

        Person p2 = new Person();
        p2.name = "阿朱";
        p2.age = 19;

        System.out.println(p1.name + "," + p1.age);
        System.out.println(p2.name + "," + p2.age);
        System.out.println("----------------------------------------");
        System.out.println(p1.totalNum); // 底层依然使用Person.totalNum来访问.
        System.out.println(p2.totalNum);
        System.out.println(Person.totalNum);
        System.out.println("----------------------------------------");
        p1.totalNum = 10;
        System.out.println(p1.totalNum); // 10
        System.out.println(p2.totalNum); // 10
        System.out.println(Person.totalNum); // 10
    }
}

Servant

// 描述菲佣信息
class Servant {
    String name; // 名字
    int age; // 年龄
    // 购物
    void shopping() {
        System.out.println("购物");
    }
    // 做饭
    void cook() {
        System.out.println("做饭");
    }
    // 洗碗
    void wash() {
        System.out.println("洗碗");
    }
}
// 程序员
class Coder{
    // 写代码
    void coding() {
        System.out.println("开发一个游戏");
    }
}

// 操作菲佣对象
public class ServantDemo {
    public static void main(String[] args) {
        // 创建菲佣对象
        Servant s1 = new Servant();
        // 给对象的字段设置值
        s1.name="乔峰";
        s1.age=33;
        // 获取对象的字段的值
        Servant s2 = new Servant();
        s2.name="乔峰";
        s2.age=33;

        System.out.println(s1 == s2); // false


    System.out.println(s1.name+","+s1.age);
    System.out.println("---------------------------------");
    Servant ss2 = new Servant();
    ss2.name="西门吹雪";
    ss2.age=28;
    System.out.println(ss2.name+","+ss2.age);
    System.out.println("---------------------------------");
    Servant ss3 = new Servant();
    ss3.name="陆小凤";
    ss3.age=26;
    System.out.println(ss3.name+","+ss3.age);
    System.out.println("---------------------------------");
        // 把s2所引用的地址值赋给s1变量
    s1 = ss2;
    System.out.println(s1.name+","+s1.age);
    System.out.println(ss2.name+","+ss2.age);
        // 此时s3变量没有引用任何堆中的内存空间
    ss3 = null;
    // System.out.println(ss3.name+","+ss3.age);
    }
}

Static

// 演示static成员和非static成员的访问
public class StaticDemo {
    String msg = "非static成员变量";
    static String staticMsg = "static成员变量";
    static  String info = null;
    static  boolean flag = false;

    void doWork(){
        System.out.println(msg);
        System.out.println(staticMsg);
        staticDoWork();
    }
    static void staticDoWork() {
        System.out.println("staticDoWork");
    }
    public static void main(String[] args) {
        System.out.println(info);
        System.out.println(flag);
       // System.out.println(msg); // 错误：无法从静态上下文中引用非静态方法 变量msg
        System.out.println(staticMsg); // static成员变量
        // doWork(); // 错误：无法从静态上下文中引用非静态 方法 doWork
        staticDoWork();

        new StaticDemo().doWork();
    }
}

Student

/**
 * 需求:
 * 学生类(Student)有两个字段：name(名字)和isFee(是否交学费的状态)，有一个方法：交学费(fees)。
 * 每一个学生都是通过Student类new出来的一个对象，现在创建一个数组存放学生对象，再分别调用该数组里的这些学生交学费的方法。
 */
// 描述学生信息的类
class Student {
    String name = null; // 名称
    boolean isFee = false; // 是否已经缴学费

    // 缴学费
    void fees() {
        isFee = true; // 修改是否缴学费的状态
    }

    Student() {
        System.out.println("AA");
    }

    Student(String n) {
        name = n;
    }
}

// 测试
public class StudentDemo {
    public static void main(String[] args) {
        Student ss = new Student("小明");

        Student s1 = new Student();
        s1.name = "赵一";
        s1.isFee = false;

        Student s2 = new Student();
        s2.name = "钱二";
        // 设置已经缴学费的状态
        s2.isFee = true;

        Student s3 = new Student();
        s3.name = "孙三";
        s3.isFee = false;

        Student s4 = new Student();
        s4.name = "李四";
        s4.isFee = false;

        Student s5 = new Student();
        s5.name = "周五";
        s5.isFee = false;

        System.out.println(s5.isFee);
        // 把以上5个学生对象,存放到一个容器中(数组)
        Student[] students = new Student[]{s1, s2, s3, s4, s5};
        for (Student s : students) {
            // 判断学生是否已经缴费,若没有,则调用其缴费的方法
            if (!s.isFee) {
                s.fees(); // 缴费
            }
        }
        System.out.println(s5.isFee);

        // 集合/数组中存储元素,其实存储的是该对象的引用地址
        System.out.println(students[4] == s5); // true
    }
}

 Animal

// 动物
class Animal {
    Animal(){}
    void slepp() {
        System.out.println("睡觉,zzzzzz.......");
    }
}
// 狗
class Dog extends Animal {
    void watch() {
        System.out.println("看门.........");
        slepp();
    }
}
// 猫
class Cat extends Animal {
    void catchMouse() {
        System.out.println("逮老鼠");
        slepp();
    }
}

public class AnimalDemo {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.watch();
        Cat cat = new Cat();
        cat.catchMouse();
    }
}

Extends

// 人类
class Persons {
    String name; // 姓名
    int age; // 年龄
    // 省略Getter/Setter
}
// 老师类
class Teacher extends Persons {
    private String staffid; // 工号
    private String hirDate; // 入职时间
}
// 学生类
class Student extends Persons {
    private String stuid; // 学号
}
// 员工类
class Employee extends Persons {
    private String empid; // 工号
    private String hirDate; // 入职时间
}

public class ExtendsDemo {
    public static void main(String[] args) {
        System.out.println("Hello");
    }
}

Import

import java.util.Arrays;
import java.util.List;
import java.util.Set;

public class ImportDemo {
    public static void main(String[] args) {
        int[] arr1 = {1,2,3,4,5};

        String ret = Arrays.toString(arr1);
        System.out.println(ret);

        System.out.println(Arrays.toString(arr1));
        Set set = null;
        List list = null;

        System.out.println(Math.max(30,20)); // 最大值
        System.out.println(Math.min(30,20)); // 最小值
    }
}

Object

class Duck {
    private String name = "小丑鸭";
    private int age = 11;
    // 覆盖Object的toString方法
    public String toString(){
        return this.name+","+this.age;
    }
}

public class ObjectDemo {
    public static void main(String[] args) {
        String str1 = "AA";
        String str2 = "AA";
        System.out.println(str1 == str2); // true
        System.out.println("-----------------");
        String s1 = new String("AA");
        String s2 = new String("AA");
        System.out.println(s1 == s2); // false
        System.out.println("------------------");
        boolean ret = s1.equals(s2);
        System.out.println(ret); // true
        System.out.println("--------------");
        Duck duck = new Duck();
        System.out.println(duck); // 小丑鸭,11
        System.out.println(duck.toString()); // 小丑鸭,11
    }
}

Override

// 鸟类
class Bird {
    protected void fly() {
        System.out.println("我要飞得更高！！！");
    }
}

// 企鹅
class Penguin extends Bird {
    @Override
    public void fly() {
        System.out.println("我是折翼的天使,飞不动！！！");
    }
    // 企鹅特有的方法
    public void swimming() {
        super.fly();
        System.out.println("游泳,很凉快...");
    }
}

// 方法的覆盖
public class OverrideDemo {
    public static void main(String[] args) {
        Penguin p = new Penguin();
//        p.fly();
        p.swimming();
    }
}

Person

class Person{
    String name;
    int age;
    // 专门给age字段设置值
    public void setAge(int a) {
        if (a < 0) {
            System.out.println("年龄不能为负数");
            return;// 结束方法
        }
        age = a;
    }
}
// 封装思想
public class PersonDemo {
    public static void main(String[] args) {
        // 创建一个Person对象,给年龄赋值,再打印年龄值
        Person p1 = new Person();
        // 数据不合理,没有做检查
        p1.setAge(-16);
        System.out.println(p1.age);
    }
}
class Person2{
    private String name = "小明";
    private int age;
    // 向外暴露获取name的值
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int a) {
        if (a<0) {
            System.out.println("年龄不能小于0");
            return;
        }
        age = a;
    }
}

// 封装思想
public class PersonDemo2 {
    public static void main(String[] args) {
        Person2 p = new Person2();
        p.setName("Will");
        String name = p.getName();
        p.setAge(17);
        System.out.println(name);
    }
}

Super

// 父类
class SuperClass{
    SuperClass(){
        System.out.println("SuperClass构造器....");
    }
}
// 子类
class SubClass extends SuperClass{
    SubClass() {
        super(); // 默认会调用父类无参数构造器
        System.out.println("SubClass构造器....");
    }
}

// super关键字
public class SuperDemo {
    public static void main(String[] args) {
        // 创建子类对象
        SubClass sub = new SubClass();
    }
}
// 动物
class Animals {
    private String name;
    private int age;
    Animals(String name, int age) {
        this.name = name;
        this.age = age;
    }
    public void say() {
        System.out.println(this.name + ",今年" + this.age + "岁");
    }
}
// 鱼
class Fish extends Animals {
    private String color; // 颜色
    Fish(String name, int age, String color) {
        super(name, age); // 调用父类构造器
    }
    // 说：名字,年龄,颜色
    public void say() {
        super.say(); // 调用父类的say方法
        System.out.println("我的颜色是" + color);
    }
}

public class SuperDemo2 {
    public static void main(String[] args) {
        Fish f = new Fish("尼莫", 3, "红色");
        f.say();
    }
}

This

public class ThisDemo {
    private String name = "成员变量";
    private int age;

    public ThisDemo() {
        this(null, 0); // 调用ThisDemo(String name, int age)
        System.out.println("无参数构造器");
    }

    public ThisDemo(String name) {
        this(); // 调用ThisDemo()
        System.out.println(111);
    }

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

    public void show() {
        System.out.println("show方法");
    }

    public ThisDemo append() {
        return this;
    }

    public void doWork() {
        this.show();
        String name = "局部变量";
        System.out.println(name); // 局部变量
        System.out.println(this.name); // 成员变量
    }

    public static void main(String[] args) {
        new ThisDemo("乔峰", 25);
    }
}
// 描述了用户对象
class User{
    private String name;
    private int 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 UserDemo {
    public static void main(String[] args) {
        // 创建一个User对象,给该对象设置名字为Lucy
        User u1 = new User();
        u1.setName("Lucy");
        System.out.println(u1.getName());
    }
}

Abstract

// 圆形
class Graph{
    // 图像都有求面积的行为
    public double getArea(){
        return 0.0;
    }
}
// 圆
class Circle{
    private int r; // 半径
    Circle(int r){
        this.r = r;
    }
    // 求面积
    public double getArea(){
        return 3.14 * r * r;
    }
}
// 矩形
class Rectangle{
    private int width;
    private int height;
    Rectangle(int width,int height){
        this.width = width;
        this.height = height;
    }
    // 求面积
    public double getArea(){
        return width * height;
    }
}

// 三角形
class Triangle extends Graph {
    private Integer a;
    private Integer b;
    private Integer c;
    Triangle(Integer a, Integer b, Integer c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }
    // 求面积
    public double getArea() {
        // 秦九昭公式
        return 100;
    }
}

public class AbstractDemo {
    public static void main(String[] args) {
        // 求圆的面积
        System.out.println("圆的面积");
        System.out.println(new Circle(10).getArea()); // 314.0
        // 求矩形的面积
        System.out.println("矩形的面积");
        System.out.println(new Rectangle(10,6).getArea()); // 60.0
        // 求三角形的面积
        System.out.println("三角形面积");
        Triangle tri = new Triangle(3,4,5);
        System.out.println(tri.getArea()); // 100.0

    }
}

Animal

// 动物类
class Animal {
    public void eat() {
        System.out.println("吃一般的食物");
    }
}
// 狗类
class Dog extends Animal {
    public void eat() {
        System.out.println("吃狗粮...");
    }
    public void watch() {
        System.out.println("看门...");
    }
}
// 猫类
class Cat extends Animal {
    public void eat() {
        System.out.println("吃猫粮...");
    }
    public void catchMouse(){
        System.out.println("逮老鼠....");
    }
}

// 人类
class Person {
    // 喂养任何动物
    public void feed(Animal a) {
        // 判断a是Dog类型还是Cat类型,不同的类型完成不同的功能
        System.out.println("....feeding....");
        a.eat(); // 吃食物
        if (a instanceof Dog) {
            Dog d = (Dog) a; // 强转
            d.watch();
        } else if (a instanceof Cat) {
            Cat c = (Cat) a; // 强转
            c.catchMouse();
        }
    }
}
public class AnimalDemo {
    public static void main(String[] args) {
        // 创建一个饲养员对象
        Person p = new Person();
        p.feed(new Dog());
        System.out.println("----------");
        p.feed(new Cat());
    }
}

Code

// 代码块
public class CodeDemo {
    {
        System.out.println("初始化代码块");
    }
    CodeDemo(){
        System.out.println("构造器");
    }

    static {
        System.out.println("静态代码块");
    }
    public static void main(String[] args) {
        System.out.println("....main......");
        if (true) {
            System.out.println("局部代码块");
        }
        new CodeDemo();
    }
}

Final

class SuperClass {
    SuperClass() {
        init();
    }
    public void init() {
        System.out.println("初始化操作");
    }
}
class SubClass extends SuperClass {
    // 覆盖
    public void init() {
        System.out.println("做自己的初始化操作");
    }
}
// final修饰符
public class FinalDemo {
    public static void main(String[] args) {
        final User user = new User();
        System.out.println(user);
        user.setName("乔峰");
        System.out.println(user);
    }
}
class User{
    String name="小明";
    public void setName(String name) {
        this.name = name;
    }
    // 覆盖
    public String toString() {
        return this.name;
    }
}

FlyWeight

// 包装类的缓存机制
public class FlyWeightDemo {
    public static void main(String[] args) {
        Integer i1 = 125;
        Integer i2 = 125;
        // 判断两个Integer是否相等
        // 比较是两个对象使用引用同一块内存空间
        System.out.println(i1 == i2); // true
        // 比较内容
        System.out.println(i1.equals(i2)); // true
        System.out.println("----------------");

        Integer i3 = new Integer(125);
        Integer i4 = new Integer(125);

        System.out.println(i3 == i4); // false
        System.out.println(i3.equals(i4)); // true
    }
}

Integer

public class IntegerDemo {
    public static void main(String[] args) {
        // 装箱/拆箱
        Integer num1 = new Integer(17);
        int num5 = num1.intValue();
        Integer num2 = Integer.valueOf(17);
        // 自动装箱/拆箱
        Integer num3 = 17;
        int um4 = num3;
        System.out.println(num5 == num1); // true
        System.out.println(num2 == num1); // false
        System.out.println(num5 == num2); // true
        System.out.println(um4==num1); // true
        Integer num = 3;
        switch (num) {
            case 1:
                break;
            case 2:
                break;
            case 3:
                break;
        }
        System.out.println("=====================");
        System.out.println(Integer.MAX_VALUE); // 2147483647

    }
}

IntWapper

// 设计int类型的包装类
class IntWapper {
    private int value; // 被包装的int值
    // int的最大/小值
    public static final int MAX_VALUE = 2147483647;
    public static final int MIN_VALUE = -2147483648;
    IntWapper(int value) {
        this.value = value;
    }
    // 转换为二进制
    public String toBinaryString(int value) {
        return "OB00100101";
    }
}

public class IntWapperDemo {
    public static void main(String[] args) {
        IntWapper wapper1 = new IntWapper(17); // 包装17
        IntWapper wapper2 = new IntWapper(95); // 包装95
        System.out.println(IntWapper.MAX_VALUE); // 2147483647
        System.out.println(IntWapper.MIN_VALUE); // -2147483648
    }
}

ClassInClass

class MyLinkedList {
    // 非静态内部类
    class MyNode1 {}
    // 静态内部类
    static class MyNode2 {}
}

class Tiger implements IWalkable {
    public void walk() {
        System.out.println("老虎走路");
    }
}

public class ClassInClassDemo {
    public static void main(String[] args) {
        // 局部内部类
        class MyClass3 {}
        // 需求：调用xxx类中的show方法
        // xxx.show(new Tiger());
        // 需求：不想为Dog类定义,只想使用一次就行了
        xxx.show(new IWalkable() {
            public void walk() {
                System.out.println("狗狗走路");
            }
        });
    }
}

class xxx {
    public static void show(IWalkable animal) {
        animal.walk();
    }
}

EnumMock

// 员工
class Employee {
    // 休息日
    private Weekday restDay;
    public Weekday getRestDay() {
        return restDay;
    }
    public void setRestDay(Weekday restDay) {
        this.restDay = restDay;
    }
}

// 专门用于表示周1到周7
enum  Weekday {
    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY;
}

public class EnumMock {
    public static void main(String[] args) {
        // 创建一个员工对象,设置一个休息日(星期几)
        Employee e = new Employee();
        e.setRestDay(Weekday.SATURDAY); // 周1休息
        if (e.getRestDay() == Weekday.SATURDAY || e.getRestDay() == Weekday.SUNDAY) {
            System.out.println("周末休息");
        } else {
            System.out.println("周1到周5休息");
        }
        System.out.println("---------------");
        // 获取枚举类型所有的对象常量
        Weekday[] days = Weekday.values();
        System.out.println(days.length);
        // 2):把一个字符串转换为枚举的常量对象
        Weekday saturday = Weekday.valueOf("SATURDAY");
        System.out.println(saturday);
        System.out.println(saturday.name());
        System.out.println(saturday.ordinal());
        System.out.println("-------------------");
        switch (Weekday.MONDAY) {
            case MONDAY :
                System.out.println("周一");
                break;
            case THURSDAY :
                System.out.println("周四");
                break;
        }
    }
}

Interface

// 可以走路的行为
interface IWalkable {
    void walk();
}

// 会游泳
interface ISwimable {
    void swim();
}

// 鱼
class Fish implements ISwimable {
    public void swim() {
        System.out.println("游啊游...");
    }
}

// 猫具有走路的行为
class Cat implements IWalkable {
    public void walk() {
        System.out.println("走猫步....");
    }
}

// 青蛙
class Frog implements ISwimable, IWalkable {
    public void walk() {
        System.out.println("跳步..");
    }

    public void swim() {
        System.out.println("..蛙泳..");
    }
}

public class InterfaceDemo {
    public static void main(String[] args) {
        // 多态：接口和实现的关系
        IWalkable cat = new Cat();
        cat.walk();

        ISwimable fish = new Fish();
        fish.swim();

        Frog frog = new Frog();
        frog.swim();
        frog.walk();
    }
}

TotalTime

// 操作模板
abstract class OperateTemplate {
    // 模板方法：提供了统一的算法骨架
    public final long getTotalTime() {
        // 1.获取当前系统时间毫秒数
        long begin = System.currentTimeMillis();
        // 2.各自的操作(累加/连接)
        doWork(); // 子类具有的操作
        // 3.获取当前系统时间毫秒数
        long end = System.currentTimeMillis();
        // 4.返回时间差(第二步操作耗时)
        return end - begin;
    }
    // 专门留给子类去实现(不同的子类实现细节不同)
    abstract protected void doWork();
}

// int类型操作
class IntOperate extends OperateTemplate {
    public void doWork() {
        long total = 0; // 总和
        for (int i = 1; i <= 50000; i++) {
            total += i; // 累加
        }
    }
}
// String操作
class StringOperate extends OperateTemplate {
    public void doWork() {
        String str = "";
        for (int i = 1; i <= 50000; i++) {
            str = str + i;
        }
    }
}
// 计算操作耗时
public class TotalTimeDemo {
    public static void main(String[] args) {
        System.out.println(new IntOperate().getTotalTime());
        System.out.println(new StringOperate().getTotalTime());
    }
}
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原文地址：https://www.cnblogs.com/zengqinghong/p/11827917.html