猿创征文 | 【Java进阶】详解抽象类及常用接口

public class TestDemo {
    public static void main(String[] args){
        Circle c = new Circle();
        c.setR(5);
        c.getArea();
        Squre s = new Squre();
        s.setLength(10);
        s.getArea();
    }
}
//抽象类
abstract class Shape{
    private int size;
    //抽象方法
    abstract public void getArea();
}
class Circle extends Shape{
    private int r;
    public int getR() {
        return r;
    }
    public void setR(int r) {
        this.r = r;
    }
    //重写抽象方法
    @Override
    public void getArea() {
        double  area = r*r*r*4.0/3;
        System.out.println("此圆形的面积是: "+area);
    }
}
class Squre extends Shape{
    private int length;
    //重写抽象方法
    @Override
    public void getArea() {
        double area = length*length;
        System.out.println("此正方形的面积是: "+area);
    }
    public int getLength() {
        return length;
    }
    public void setLength(int length) {
        this.length = length;
    }
}

//接口的定义
interface USB {
    void openDevice();
    void closeDevice();
}
//实现接口
class Mouse implements USB {
    @Override
    public void openDevice() {
        System.out.println("打开鼠标");
    }
    @Override
    public void closeDevice() {
        System.out.println("关闭鼠标");
    }
    public void click(){
        System.out.println("鼠标点击");
    }
}
//实现接口
class KeyBoard implements USB{
//实现接口中的抽象类
    @Override
    public void openDevice() {
        System.out.println("打开键盘");
    }
    @Override
    public void closeDevice() {
        System.out.println("关闭键盘");
    }
    public void inPut(){
        System.out.println("键盘输入");
    }
}

interface IRing {
    void run();
} 
interface ISing {
    void swim();
} 
interface IAmphibious extends IRunning, ISwimming {}
class Frog implements IAmphibious {
    @Override
    public void run() {
        System.out.println("跑啊跑");
    }
    @Override
    public void swim() {
        System.out.println("游啊游");
    }
}

public class TestDemo5 {
    public static void main(String[] args) {
        function(new Person());
        function(new Student());
    }
    public static void function(Object obj){
        System.out.println(obj);
    }
}
class Person{
    private int age;
    private String name;
}
class Student{
    private int grade;
    private String sno;
}

//Object类中的toString()方法实现：
public String toString() {
     return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

public native int hashCode();

class Per{
    public String name;
    public int age;
    public Per(String name, int age) {
        this.name = name;
        this.age = age;
    }
    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
}
public class TestDemo6 {
    public static void main(String[] args) {
        Per per1 = new Per("gaobo",20);
        Per per2 = new Per("gaobo", 20);
        System.out.println(per1.hashCode());
       /* 
        注意事项：哈希值一样。
        结论：
        1、hashcode方法用来确定对象在内存中存储的位置是否相同
        2、事实上hashCode() 在散列表中才有用，在其它情况下没用。
        在散列表中hashCode() 的作用是获取对象的散列码，进而确定该对象在散列表中的位置。
        */
        System.out.println(per2.hashCode());
    }
}

// Object类中的equals方法
​
public boolean equals(Object obj){
​
     return (this == obj);
   // 使用引用中的地址直接来进行比较
   
}

@Override
 public boolean equals(Object obj) {
     //判断是否为空
        if (obj == null) {
            return false ;
        } if(this == obj) {
            return true ;
        }
        // 不是Person类对象
        if (!(obj instanceof Per)) {
            return false ;
        }
        Per per = (Per) obj ; // 向下转型，比较属性值
        return this.name.equals(per.name) && this.age==per.age ;
    }
    
/*  @Override
    public boolean equals(Object obj) {
        Per per = (Per)obj;
        //String类调用的是自身的equals，
        // s1跟s2两者比较的规则则是按照String类重写后的equals方法来比较，
        //很显然，String类的比较规则是按照值来比较的，因此结果会输出true。
        if(this.name.equals(per.name)&&this.age == per.age){
                return true;
        }
        return false;
​
    }
}
*/

@Override
public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Per per = (Per) o;
        return age == per.age &&
                Objects.equals(name, per.name);
    }
    @Override
    public int hashCode() {
        return Objects.hash(name, age);
   }

String x = "string";
String y = "string";
String z = new String("string");
System.out.println(x==y); // true
System.out.println(x==z); // false
System.out.println(x.equals(y)); // true
System.out.println(x.equals(z)); // true

public boolean equals(Object obj) {
        return (this == obj);
}

class Student {  
    String name;
    int age;
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
    @Override  
    public String toString() { 
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
public class test4 {
    public static void main(String[] args) {
        Student[] students = new Student[] { 
              new Student("zhangsan", 13),
              new Student("lisi", 23),
              new Student("able", 17),
        };
        Arrays.sort(students);
        System.out.println(Arrays.toString(students));
       }
}

class Student implements Comparable{
    public int age;
    public String name;
    
    public Student(int age, String name) {
        this.age = age;
        this.name = name;
    }
    @Override
    public String toString() {
        return "Student{" +
                "age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
    //重写compareTo方法
    @Override
    public int compareTo(Student o) {
        if (this.age - o.age > 0)
            return 1;
        else
        if (this.age - o.age < 0)
            return -1;
        else
            return 0;
    }
     public static void main1(String[] args) {
        Student student = new Student(16, "liba");
        Student student1 = new Student(13, "zhangsan");
        System.out.println(student.toString());
        System.out.println(student1.toString());
        if (student.compareTo(student1) > 0) {
            System.out.println("student > student1");
        } else {
            System.out.println("student < student1");
        }
    }
​
}

@Override 
 public int compareTo(Student o) {   // this.代表对当前对象的引用，o.代表对参数对的引用
        if (this.name.compareTo(o.name) > 0)//String类中重写了compareTo方法，可直接使用
             return 1;  
        else if (this.name.compareTo(o.name) < 0) 
             return -1;
        else 
             return 0;
    }
    //如果当前对象应排在参数对象之前, 返回小于 0 的数字;
    //如果当前对象应排在参数对象之后, 返回大于 0 的数字;
    //如果当前对象和参数对象不分先后, 返回 0;

class Student { 
    String name;
    int age;
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
 
    @Override  
    public String toString() {
        return "[" + this.name + ":" + this.age + "]";
    }
}
 // 实现Comparator接口中的compare方法
class AgeComparator implements Comparator { // 年龄比较器
    @Override 
    public int compare(Student o1, Student o2) {
        return o1.age - o2.age;
    // 反正返回的也是数字，当o1.age>o2.age时返回大于零的数，即o1对象排在o2对象的后面，升序排列，我们之前用Comparable接口时也可以这样简写
    }
}
public class test4 {
    public static void main(String[] args) {
        Student[] students = new Student[]{ 
                new Student("zhangsan", 13),
                new Student("lisi", 23),
                new Student("able", 17),
        };
        AgeComparator ageComparator = new AgeComparator(); 
        Arrays.sort(students, ageComparator); 
        // 用类Arrays.sort对students数组进行排序，这里传了两个参数（学生对象和所对应的年龄比较器）
        System.out.println(Arrays.toString(students));
    }
}

class Student {
    String name;
    int age;
 
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
    @Override  
    public String toString() {
        return "[" + this.name + ":" + this.age + "]";
    }
}
class NameComparator implements Comparator { // 姓名比较器
    // 实现Comparator接口中的compare方法
    @Override  
    public int compare(Student o1, Student o2) {
        return o1.name.compareTo(o2.name); 
// 因为name是String类型，也是一个引用类型，也要用到compareTo方法，此时的compareTo方法是String类里重写的方法
    }
}
public class test4 {
    public static void main(String[] args) {
        Student[] students = new Student[]{ 
                new Student("zhangsan", 13),
                new Student("lisi", 23),
                new Student("able", 17),
        };
        NameComparator nameComparator = new NameComparator();
        Arrays.sort(students, nameComparator);  
        System.out.println(Arrays.toString(students));
      }
}

class Student {
    public int age = 15;
    @Override 
    public String toString() {
        return "Student{" +
                "id=" + id +
                '}';
    }
}
public class test3 {
    public static void main(String[] args) {
        Student student1 = new Student();
        System.out.println(student1);
    }
}

Student student2 = student1;

class Student implements Cloneable{
    public int age = 10;
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
    @Override
    public String toString() {
        return "Person{" +
                "age=" + age +
                '}';
    }
}
public class Demo2 {
    public static void main(String[] args) throws CloneNotSupportedException{
        Student student = new Student();
        Student student2 = (Student)student.clone();   //返回值为Object需要进行强制类型转换
        System.out.println(student.age);
        System.out.println(student2.age); 
        student2.age = 18;
        System.out.println(student.age);
        System.out.println(student2.age);
    }
}

class Teacher{
    int number = 20;
}
class Student implements Cloneable{
    public int age = 10;
    Teacher teacher = new Teacher();
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
​
    @Override
    public String toString() {
        return "Person{" +
                "age=" + age +
                '}';
    }
}
public class Demo2 {
    public static void main(String[] args) throws CloneNotSupportedException{
        Student student = new Student();
        Student student2 = (Student)student.clone();   //返回值为Object需要进行强制类型转换
​
        System.out.println(student.teacher.number);
        System.out.println(student2.teacher.number);
​
        student.teacher.number = 100;
        
        System.out.println(student.teacher.number);
        System.out.println(student2.teacher.number);
​
    }
}

class Teacher implements Cloneable{
    int number = 20;
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}
class Student implements Cloneable{
    public int age = 10;
    public Teacher teacher = new Teacher();
    @Override
    protected Object clone() throws CloneNotSupportedException {
        //  此时我们在进行 “(Student) student.clone();” 操作，
        //  我们在堆上对student克隆拷贝出来一个新对象，并让引用变量tmp指向新对象
        Student tmp = (Student) super.clone();
        // 用this.teacher.clone()对引用变量teacher所指向的Teacher类对象进行克隆
        tmp.teacher = (Teacher) this.teacher.clone();
        return tmp;
    }
    @Override
    public String toString() {
        return "Person{" +
                "age=" + age +
                '}';
    }
}
public class Demo2 {
    public static void main(String[] args) throws CloneNotSupportedException{
        Student student = new Student();
        // 此时的student.clone返回Student类对象的引用tmp,student2 就指向了原来tmp所指向的对象
        Student student2 = (Student)student.clone();  
​
        System.out.println(student.teacher.number);
        System.out.println(student2.teacher.number);
        student.teacher.number = 100;
        System.out.println(student.teacher.number);
        System.out.println(student2.teacher.number);
​
    }
}