java类的特性

1.封装

package test;
//封装
public class PackageTest {
    //第一步：私有
    private String name ;
    private int age;
    //第二步：公开方法
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        //第三步：限制条件
        if(age>30){
            this.age = 18;
            System.out.println("你想知道的太多了");
        }
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }

}

2.继承

//父类
package heinika;
public class Animal {
    public void voice(){
        System.out.println("动物叫！！！");
    }
}
//子类
package heinika;

public class Cat extends Animal{
    public static int eyesNum = 2;
    public static void sleep(){
        System.out.println("我在睡觉");
    }
    @Override
    public void voice() {
        System.out.println("喵喵叫！！");
    }

    public void voice(String voice) {
        System.out.println(voice);
    }

    public void voice(int voice) {
        System.out.println(voice);
    }
}


package heinika;

public class Dog extends Animal {
    public Dog() {
        this("red");
        //调用本类的构造器，必须写在第一行
        //super,调用父类的构造器，必须写在第一行
    }

    public Dog(String color) {
    }

    public void voice() { // 重写父类方法
        System.out.println("汪汪汪！！！");
    }
}

package heinika;

public class Student {
    private int id;
    private String name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public static Dog wangCai = new Dog();
    public static int add(int a,int b){
        return a+b;
    }
    @Override
    public String toString() {
        return "我是一名学生";
    }
//  @Override
//  public int hashCode() {
//      return super.hashCode();
//  }
    @Override
    public boolean equals(Object obj) {
        if(obj!=null){
            if(obj instanceof Student){
                boolean isSameStudent  =  this.id==((Student)obj).id;
                return  isSameStudent;
            }
        }
        return false;
    }
}

3.多态

package heinika;

public class Test {

    public static void main(String[] args) {
        //子类中复写父类的方法
        Animal animal = new Animal();
        animal.voice();
        Dog dog = new Dog();
        dog.voice();
        //多态，父类引用子指向类对象，根据对象的不同产生的结果不同
        Animal animal2 = new Cat();
        Animal animal3 = new Dog();
        animal2.voice();
        animal3.voice();
        ((Cat)animal2).voice("maiomiao~~");
        if(animal2 instanceof Cat){
            ((Cat)animal2).voice(666666666);
        }
        //方法的重载,方法名相同，所带参数个数或类型不同
        Cat cat = new Cat();
        cat.voice();
        cat.voice("呵呵");
        cat.voice(1223);


        //静态
        /*System.out.println(Cat.eyesNum);
        Cat.sleep();
        Student.wangCai.voice();
        System.out.println(Student.add(1, 2));  */  
        Student student1 = new Student();
        Student student2 = new Student();
        student1.setName("zhangsan");
        student2.setName("lisi");
        student1.setId(23);
        student2.setId(23);
        System.out.println(student1.equals(student2));
        System.out.println(student1);
        System.out.println(Integer.parseInt("3C", 16));
    }   
}