public class Animals {  //父类private String lei;private double weight;  //需要get,set一下,外界才可以调用public Animals() {}public Animals(String lei, double weight) {super();this.lei = lei;this.weight = weight;}public void Print() {System.out.println("动物种类" + lei);System.out.println("重量" + weight);}/*public void Sv () {System.out.println("你好");}*/public String getLei() {return lei;}public void setLei(String lei) {this.lei = lei;}public double getWeight() {return weight;}public void setWeight(double weight) {this.weight = weight;}}

public class Dog extends Animals {  //子类private String shi;public Dog() {}public Dog(String lei, double weight,String shi) {super(lei, weight);   //引用的是父类里的lei,weight构造方法this.shi = shi;}public void Print () {  //重写父类里的方法System.out.println("动物种类是" + super.getLei()); //因为是继承,super之后就可以获取System.out.println("重量" + super.getWeight());System.out.println("狗的食物"+ shi);}public String getShi() {return shi;}public void setShi(String shi) {this.shi = shi;}}

public class Main {public static void main(String[] args) {//父类的引用指向子类对象Animals an = new Dog();  //实例化Animalsan.setLei("狗");  an.setWeight(15);/*an.Print();*///父类里的方法,要想设置食物,走下一步强转Dog dg = (Dog) an;  //子类Dog新增的属性shi和方法,不能直接访问,要强转dg.setShi("骨头");dg.Print();}}

public class Test {public void Printf(Animals an) {  //多态if(an instanceof Dog) {  //如果an这个对象是一种狗,//instanceof关键字是用来判断变量an是不是这个类或是这个类的子类Dog x =(Dog)an;  //强转成狗x.Print();   //输出Dog的构造方法} else if(an instanceof Cat ) {Cat c = (Cat)an;  //强转成猫c.Print();//输出Cat的构造方法}else {an.Print();  //animals的方法}}

}

//多态Dog dog = new Dog("狗",15,"骨头");  //先实例化一个DogCat cat = new Cat("猫",5,"老鼠");Test t = new Test();t.Printf(dog);  //dog就是an的一种t.Printf(cat);

public class Dog extends Animals {  //子类//static 静态private String name;private int age;public static  int num;  //staticpublic Dog() {  //给num一个构造方法num++;}public void Print () {System.out.println("这是第" + num + "只狗");}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;}}

//static 的静态利用Dog d1 = new Dog();d1.Print(); //输出第几只狗System.out.println(Dog.num);  //static 直接拿类名 . num 输出,输出第一个狗Dog d2 = new Dog();System.out.println(Dog.num); //输出第二只狗d2.Print();

public class HelloWorld {private static HelloWorld helloworld;private HelloWorld () {}private int count;public static HelloWorld getinstance() {  //static的不用实例化,直接用if (helloworld == null ) {    //如果helloworld是空的话helloworld = new HelloWorld();  //给helloworld实例化}return helloworld;    //返回helloworld}public int getCount() {return count;}public void setCount(int count) {this.count = count;}}

//单例模式HelloWorld hw = HelloWorld.getinstance();System.out.println(hw.getCount());  //输出的返回值是为0,因为没有给其赋值HelloWorld hw2 = HelloWorld.getinstance();hw2.setCount(5);System.out.println(   hw.getCount());*///输出的是5,因为hw与hw2指向的位置相同