创建一个Dog类，属性public String color; public String size; public int age;
编写他的全构造方法。在Test类测试中去用全构造方法实例化的方式进行属性的初始化，并把这个属性打印出来(tostring)

Dog.java

package com.td;

public class Dog {
    public String color;
    public String size;
    public int age;


    public Dog(String size, String color, int age){      //全构造方法   
        this.color=color;
        this.size=size;
        this.age=age;
    }
    @Override
    public String toString() {
        return "Dog{" +
                "color='" + color + '\'' +
                ", size='" + size + '\'' +
                ", age=" + age +
                '}';
    }
}

Test.java

package com.td;
public class test {
    public static void main(String[] args) {
        Dog dog = new Dog("大", "白", 19);
        System.out.println(dog);

    }
}

创建一个Cat类，属性private String color; privateString size; privateint age;
点出他所有属性的set和get 方法。在Test类测试中去用空构造方法去实例化对象之后，通过set的方法去给这个对象的所有属性赋值，并把这个属性打印出来(tostring)。

Cat.java

package com.td;

public class Cat {
    private String color;
    private String size;
    private int age;

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getSize() {
        return size;
    }

    public void setSize(String size) {
        this.size = size;
    }

    public int getAge() {
        return age;
    }

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

    @Override
    public String toString() {
        return "Cat{" +
                "color='" + color + '\'' +
                ", size='" + size + '\'' +
                ", age=" + age +
                '}';
    }
}

Test2.java

package com.td;

public class test2 {
    public static void main(String[] args) {
        Cat cat=new Cat();//空构造方法
        cat.setAge(3);
        cat.setColor("白");
        cat.setSize("小");

        System.out.println(cat);
    }

}

继承——使用关键字extends

Animal类

####Animal类
package com.td;

public class Animal {
    private String color;
    private String size;
    private int age;

    public Animal(String color, String size, int age) {
        this.color = color;
        this.size = size;
        this.age = age;
    }

    public void eat(){
        System.out.println("动物会吃");
    }
    public void sleep(){
        System.out.println("动物会睡觉");
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getSize() {
        return size;
    }

    public void setSize(String size) {
        this.size = size;
    }

    public int getAge() {
        return age;
    }

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

    @Override
    public String toString() {
        return "Animal{" +
                "color='" + color + '\'' +
                ", size='" + size + '\'' +
                ", age=" + age +
                '}';
    }
}

Dog类（继承了animal类）

package com.td;

public class Dog extends Animal{


    public Dog(String color, String size, int age) {  //无法自动继承父类的构造函数，需要自己定义
        super(color, size, age);
    }
//  public void eat(){               可以自己重写父类的方法
        System.out.println("狗不仅会吃，还会吃骨头");
    }

}

Test类

package com.td;


public class test {
    public static void main(String[] args) {
        Dog dog=new Dog("白","小",4);
        dog.eat();              //方法是可以继承的
//        Aniaml dog2=new Animal;    可以用父类去实例化对象
//        dog2.eat();
        System.out.println(dog);

        dog.setSize("大");
        System.out.println(dog.getSize());
    }
}