158 lines
2.8 KiB
Markdown
158 lines
2.8 KiB
Markdown
# 面向对象编程
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## 类与对象
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### 类的定义
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```java
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public class Person {
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// 属性（字段）
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private String name;
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private int age;
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// 构造方法
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public Person(String name, int age) {
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this.name = name;
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this.age = age;
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}
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// 方法
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public void sayHello() {
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System.out.println("你好，我是" + name);
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}
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// Getter和Setter
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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}
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```
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### 创建对象
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```java
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Person person = new Person("张三", 25);
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person.sayHello(); // 你好，我是张三
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person.setName("李四");
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System.out.println(person.getName()); // 李四
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```
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## 封装
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封装是面向对象的三大特性之一，通过访问修饰符控制类的成员访问权限。
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| 修饰符 | 同一类 | 同一包 | 子类 | 其他 |
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|--------|--------|--------|------|------|
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| public | ✓ | ✓ | ✓ | ✓ |
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| protected | ✓ | ✓ | ✓ | ✗ |
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| default | ✓ | ✓ | ✗ | ✗ |
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| private | ✓ | ✗ | ✗ | ✗ |
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## 继承
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```java
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// 父类
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public class Animal {
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protected String name;
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public Animal(String name) {
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this.name = name;
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}
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public void eat() {
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System.out.println(name + "正在吃东西");
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}
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}
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// 子类
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public class Dog extends Animal {
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public Dog(String name) {
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super(name);
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}
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public void bark() {
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System.out.println(name + "正在汪汪叫");
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}
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}
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// 使用
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Dog dog = new Dog("旺财");
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dog.eat(); // 旺财正在吃东西
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dog.bark(); // 旺财正在汪汪叫
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```
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## 多态
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```java
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public class Shape {
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public void draw() {
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System.out.println("绘制图形");
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}
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}
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public class Circle extends Shape {
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@Override
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public void draw() {
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System.out.println("绘制圆形");
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}
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}
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public class Rectangle extends Shape {
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@Override
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public void draw() {
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System.out.println("绘制矩形");
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}
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}
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// 多态使用
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Shape shape1 = new Circle();
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Shape shape2 = new Rectangle();
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shape1.draw(); // 绘制圆形
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shape2.draw(); // 绘制矩形
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```
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## 抽象类与接口
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### 抽象类
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```java
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public abstract class Vehicle {
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protected String brand;
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public Vehicle(String brand) {
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this.brand = brand;
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}
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// 抽象方法
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public abstract void start();
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// 具体方法
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public void showBrand() {
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System.out.println("品牌：" + brand);
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}
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}
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```
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### 接口
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```java
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public interface Flyable {
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void fly();
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default void show() {
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System.out.println("可以飞行");
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}
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}
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public class Bird implements Flyable {
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@Override
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public void fly() {
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System.out.println("鸟在飞翔");
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}
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}
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```
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