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类的定义、类的继承、多态、样例类

code • 2022-5-6 • java • 阅读 24

类的定义、类的继承、多态、样例类,第1张

/**
 * Java中的类
 * 可以在类中定义属性、方法
 */
public class Demo02StudentJava {
    String id;
    String name;
    int age;
    String clazz;

    //构造方法 对属性进行初始化
    //无参构造方法
    public Demo02StudentJava(){

    }

    //重载构造方法
    public Demo02StudentJava(String id,String name,int age){
        this.id=id;
        this.name=name;
        this.age=age;
        this.clazz="自由分班";
    }

    //重载构造方法
    public Demo02StudentJava(String id,String name,int age,String clazz){
        this.id=id;
        this.name=name;
        this.age=age;
        this.clazz=clazz;
    }

    @Override
    //重写父类的构造方法
    public String toString() {
        return "Demo02StudentJava{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

    public void printClazz(){
        System.out.println(this.name+","+this.clazz);
    }

    public static void main(String[] args) {
       //传入参数 创建对象 该对象会默认获得类中定义的属性和方法
        Demo02StudentJava stu1 = new Demo02StudentJava();
        Demo02StudentJava zs = new Demo02StudentJava("001", "zs", 20);
        System.out.println(stu1);
        System.out.println(zs);

        Demo02StudentJava ls = new Demo02StudentJava("002", "ls", 21);
        Demo02StudentJava ww = new Demo02StudentJava("003", "ww", 22,"文科一班");

        ls.printClazz();
        ww.printClazz();
    }
}

Demo02StudentJava{id='null', name='null', age=0}
Demo02StudentJava{id='001', name='zs', age=20}
ls,自由分班
ww,文科一班

/**
 * Scala中的类
 * 面向对象：封装 继承 多态
 * 也可以定义属性、方法
 * {}默认的构造方法
 */
class Demo03StudentScala(id:String,name:String,age:Int) {
  //定义属性即赋值
  val _id:String=id
  val _name:String=name
  val _age:Int=age
  var _clazz:String=_  //待会再赋值
//  var _clazz:String="自由分班" //给默认值


  //重载构造方法
  def this(id:String,name:String,age:Int,clazz:String){
    //第一行代码必须调用默认的构造方法
    this(id,name,age)
    println("重载构造方法")

    this._clazz=clazz
  }

  override def toString(): String ={
    return s"Demo03StudentScala(id=${_id},name=${_name},age=${_age})"
  }

  def printStuName():Unit={
    println(_name)
  }

  def  printClazz(): Unit ={
    println(this._clazz)
  }
}

object Demo03StudentScala{
  def main(args: Array[String]): Unit = {
    //创建对象
    val zs: Demo03StudentScala = new Demo03StudentScala("001", "zs", 20)
    val ls: Demo03StudentScala = new Demo03StudentScala("002", "ls", 21)
    println(zs)
    println(ls)
    println(zs._name)

    zs.printStuName()
    ls.printStuName()

    val ww: Demo03StudentScala = new Demo03StudentScala("003", "ww", 22)
    val xm: Demo03StudentScala = new Demo03StudentScala("004", "xm", 23,"文科二班")
    ww.printClazz()
    xm.printClazz()
  }
}

 Demo03StudentScala(id=001,name=zs,age=20)
Demo03StudentScala(id=002,name=ls,age=21)
zs
zs
ls
重载构造方法
null
文科二班

class Person(id:String,name:String,age:Int) {
  val _id:String=id
  val _name:String=name
  val _age:Int=age

  def printName(): Unit ={
    println(s"这是Person类中的对象，名字为$name")
  }

  def walk(): Unit ={
    println("人类会行走")
  }
}

class Teacher(id:String,name:String,age:Int,clazz:String) {
  val _id: String = id
  val _name: String = name
  val _age: Int = age
  val _clazz: String = clazz

  def printName(): Unit = {
    println(s"这是Teacher类中的对象，名字为$name")
  }

  def walk(): Unit ={
    println("Teacher也属于Person,也会行走")
  }
}

class Student(id:String,name:String,age:Int,gender:String,clazz:String) {
  val _id: String = id
  val _name: String = name
  val _age: Int = age
  val _gender:String=gender
  val _clazz: String = clazz

  def printName(): Unit = {
    println(s"这是Student类中的对象，名字为$name")
  }

  def walk(): Unit ={
    println("Student也属于Person,也会行走")
  }
}
class Person(id:String,name:String,age:Int) {
  val _id:String=id
  val _name:String=name
  val _age:Int=age

  def printName(): Unit ={
    println(s"这是Person类中的对象，名字为$name")
  }

  def walk(): Unit ={
    println("人类会行走")
  }

  override def toString: String ={
    return s"Person(${_id},${_name},${_age})"
  }
}

//Scala在继承父类时，需要调用父类的构造方法
class Teacher(id:String,name:String,age:Int,clazz:String) extends Person(id,name,age) {
  //对子类特有的属性做初始化
  val _clazz: String = clazz

  //父类中由同名的方法 需要加上override进行重写
  override def printName(): Unit = {
    println(s"这是Teacher类中的对象，名字为$name")
  }

  override def walk(): Unit ={
    println("Teacher也属于Person,也会行走")
  }

  override def toString: String ={
    return s"Teacher(${_id},${_name},${_age},${_clazz})"
  }
}

//继承能够获得父类定义好的属性和方法
class Student(id:String,name:String,age:Int,gender:String,clazz:String) extends Person(id,name,age){
  val _gender:String=gender
  val _clazz: String = clazz

  override def printName(): Unit = {
    println(s"这是Student类中的对象，名字为$name")
  }

  override def walk(): Unit ={
    println("Student也属于Person,也会行走")
  }

  def printGender(): Unit ={
    println(this._gender)
  }

  override def toString: String ={
    return s"Student(${_id},${_name},${_age},${_gender},${_clazz})"
  }
}

object Demo04ScalaClassExtend{
  //多态 父类引用指向子类对象
  def PersonWalkTwice(person:Person): Unit ={
    person.walk()
    person.walk()
  }

  def TeacherWalkTwice(teacher: Teacher): Unit ={
    teacher.walk()
    teacher.walk()
  }

  def StudentWalkTwice(student: Student): Unit ={
    student.walk()
    student.walk()
  }

  def main(args: Array[String]): Unit = {
    val p1: Person = new Person("001", "p1", 20)
    println(p1)
    println(p1._id)
    p1.walk()
    p1.printName()

    val t1: Teacher = new Teacher("002", "t1", 21,"文科一班")
    println(t1._clazz)

    val s1: Student = new Student("003", "s1", 22, "男", "文科二班")
    println(s1._gender)
    s1.printGender()

    PersonWalkTwice(p1)
    TeacherWalkTwice(t1)
    StudentWalkTwice(s1)

    PersonWalkTwice(t1)
    PersonWalkTwice(s1)
  }
}

 Person(001,p1,20)
001
人类会行走
这是Person类中的对象，名字为p1
文科一班
男
男
人类会行走
人类会行走
Teacher也属于Person,也会行走
Teacher也属于Person,也会行走
Student也属于Person,也会行走
Student也属于Person,也会行走
Teacher也属于Person,也会行走
Teacher也属于Person,也会行走
Student也属于Person,也会行走
Student也属于Person,也会行走

object Demo05CaseClass {
  def main(args: Array[String]): Unit = {
    val zs: CaseStudent = new CaseStudent("001", "zs", 20, "男", "文科一班")
    println(zs.id)
    println(zs.name)
    println(zs.gender)
    zs.age=21
    println(zs.age)

    println(zs)
  }
}

/**
 * 样例类
 * 实现序列化接口 可以在网络中传输
 * 所有的属性默认都是不可以修改的 如果需要修改 那么在定义的时候要使用var修饰 默认是由val修饰
 * 会重写默认的toString方法 如果直接打印 会输出对应的所有的属性值
 * 会自动给每个属性加上get、set(由var修饰的属性才会有)方法
 */
case class CaseStudent(id:String,name:String,var age:Int,gender:String,clazz:String)

 001
zs
男
21
CaseStudent(001,zs,21,男,文科一班)

import java.io.*;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
public class Demo06WordCountJava {
    public static void main(String[] args) throws IOException {
        HashMap wordMap = new HashMap<>();
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(new FileInputStream("D:\\projects\\bigdata16\\Scala\\data\\words.txt")));
        String line="";
        while ((line= bufferedReader.readLine())!=null){
            String[] words = line.split(",");
            for (String word :
                    words) {
                if(wordMap.containsKey(word)) {
                    Integer value = wordMap.get(word);
                    wordMap.put(word,value+1);
                }else {
                    wordMap.put(word,1);
                }
            }
        }
        bufferedReader.close();
        //打印结果
        Set> entrySet = wordMap.entrySet();
        for (Map.Entry entry : entrySet) {
            System.out.println(entry.getKey()+" : "+entry.getValue());
        }
    }
}

 java : 20
spark : 10
hadoop : 10

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原文地址: http://outofmemory.cn/langs/799988.html

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