JAVA基础

最新推荐文章于 2024-08-26 13:32:01 发布

原创最新推荐文章于 2024-08-26 13:32:01 发布 · 166 阅读

0 ·

CC 4.0 BY-SA版权

本文深入讲解了Java中的方法重载、构造函数、继承、抽象与多态等关键概念，并通过实例演示了异常处理、文件遍历、集合操作、多线程及迭代器的使用。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

方法重载

public class ChongZai {
   public static void main(String[] args) {
      System.out.println(add(2,3));
      System.out.println(add(1,2,3));
   }
   public static int add(int a,int b){
      return a+b;
   }
   public static int add(int a,int b,int c){
      return a+b+c;
   }
}

构造函数

public class GouZao {
   int id;
   String name;
   public GouZao(int id,String name){ //构造器与类名一致，初始化数值
      this.id=id;
      this.name=name;
   }
   public void getName(){ //方法
      System.out.println(this.name);
   }
   public static void main(String[] args) {
      GouZao g=new GouZao(3,"AAA"); //构造新对象
      g.getName();//调用方法
   }
}

继承

public class JiCheng {
   public static void main(String[] args) {
      student s=new student(3,"AA",5);
      s.play();  //子类的方法
      s.study(); //父类的方法
   }
}
class person { //父类
   int age;
   String name;
   public void study(){  //父类的方法定义
      System.out.println("FATHER");
   }
}
class student extends person{
   int number;
   public student(int age, String name,int number) { //继承父类的属性
      this.age=age;
      this.name=name;
      this.number=number;
   }  
   public void play(){ //子类的方法定义
      System.out.println("SON");
   }
}

抽象与多态

//抽象类

public abstract class animal { //定义抽象类
    abstract public void play(); //定义抽象方法
}

class dog extends animal {
    public void play() { //方法重写
        System.out.println("WANG");
    }
}

class cat extends animal {
    public void play() { //方法重写
        System.out.println("MIAO");
    }
}

//多态类

public class Test {
   public static void main(String args[]){
      animal d=new dog();  //多态
      d.play();
      animal c=new cat();  //多态
      c.play();
   }
}

接口

public class JieKou {
    public static void main(String[] args) {
    child c =new child();
    c.eat();
    c.play();
    }
}
interface good { //接口1
    double PI = 3.14;
    void play();
}
interface bad { //接口2
    double PO = 3.15;
    void eat();
}
class child implements good, bad {
    public void play() {  //重写方法1
        System.out.println("PLAY");
    }
    public void eat(){  //重写方法2
        System.out.println("EAT");
    }
}

异常处理：自己处理

public class YiChang {
    public static void main(String[] args) {
        try{
            int a;
            a=8;
            double b;
            b=a/0;
        }catch(Exception e){
            e.printStackTrace();  //打印错误信息
            System.out.println("CCC");//打印自己的信息

        }finally {
            System.out.println("FFFF");//最终必须执行
        }
    }
}

异常处理：抛出

import java.lang.Exception;
public class YiChang {
    public static void main(String[] args) {
        try{
            play();
        }catch(Exception e){ //处理异常
            e.printStackTrace();  //打印错误信息
            System.out.println("CCC");//打印自己的信息
        }
    }
    public static void play() throws Exception{  //子类抛出异常给主类
        try{
            int[] a=new int[5];
            a[7]=1;
        }finally {
            System.out.println("FFFF");
        }

    }
}

异常处理：自定义

public class MyException extends Exception{
    public MyException(String message){
        super(message);
    }
}

抛出和处理

public class TestException {
    public static void main(String[] args) {
        people p =new people();
        try{
            p.setAge(-7);
        }catch(MyException e){
            e.printStackTrace();
            System.out.println("CCC");
        }
    }
}
class people{
    private int age;
    public void setAge(int age) throws MyException{
        this.age=age;
        if(age<0){
            throw new MyException("年龄错误");
        }
    }
}

FileTree

import java.io.File;
public class FileTree {
    public static void main(String[] args) {
        File f=new File("F:/Download");
        printTree(f,0);
    }

    static void printTree(File file,int level){
        for (int i = 0; i <level ; i++) {
            System.out.print("-");
        }
        System.out.println(file.getName());
        if(file.isDirectory()){
            File[] files =file.listFiles();
            for(File tmp:files){
                printTree(tmp,level+1);
            }
        }
    }
}

ArrayList实现

public class MyArray {
    int size=0;
    Object[] list=new Object[size];
    public MyArray(){  //不带参数构造
    }
    public void add(Object obj){  //实现add方法
        size++;
        Object[] newList =new Object[size];
        System.arraycopy(list,0,newList,0,list.length);
        list=newList;
        list[size-1]=obj;

    }
    public void printArray(){ //实现打印列表
        for (int i = 0; i <list.length ; i++) {
            System.out.println(list[i]);
        }
    }
    public void printSize(){  //实现打印个数
        System.out.println(size);
    }

   //MAIN
    public static void main(String[] args) {
        MyArray ma=new MyArray();
        ma.add("ASD");
        ma.add("khk");
        ma.add("kk");
        System.out.println(ma.printSize());
    }
}

LinkedList实现

public class MyLink {
    private Node first;
    private Node last;
    private int size;

    public void add(Object obj){
        Node n =new Node();
        if(first==null){

            n.setPre(null);
            n.setObj(obj);
            n.setNext(null);
            first=n;
            last=n;
        }else{
            n.setPre(last);
            n.setNext(null);
            n.setObj(obj);
            last.setNext(n);
            last=n;
        }
        size++;
    }

    public int size() {
        return size;
    }
    //MAIN
    public static void main(String[] args) {
        MyLink ma=new MyLink();
        ma.add("ASD");
        ma.add("khk");
        ma.add("kk");
        System.out.println(ma.size());

    }
}

多线程

//线程体RUN

public class ManyProcess extends Thread {
    @Override
    public void run() {  //线程体
        for (int i = 0; i <100 ; i++) {
            System.out.println("兔子跑了"+i+"步");
        }
    }
}
class ManyProcess2 extends Thread {
    @Override
    public void run() {  //线程体
        for (int i = 0; i <100 ; i++) {
            System.out.println("乌龟跑了"+i+"步");
        }
    }
}

//执行main

public class Race {
    public static void main(String[] args) {
        ManyProcess mp=new ManyProcess();//创建对象
        ManyProcess2 mp2=new ManyProcess2();
        mp.start();
        mp2.start();
    }
}

Runnable接口实现

public class RunnableME implements Runnable {
    private int num=50;
    public static void main(String[] args) {
        RunnableME re =new RunnableME();
        Thread dl1=new Thread(re,"A");
        Thread dl2=new Thread(re,"B");
        Thread dl3=new Thread(re,"C");
        dl1.start();
        dl2.start();
        dl3.start();
    }

    @Override
    public void run() {
        while (num > 0) {
            System.out.println(Thread.currentThread().getName() + num--);
        }
    }
}

迭代器使用while

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class IteratorMe {
    public static void main(String[] args) {
        Set s=new HashSet();
        s.add("A");
        s.add("B");
        Iterator it =s.iterator();
        while(it.hasNext()){
            String st=(String)it.next();
            System.out.println(st);
        }
    }
}

迭代器使用for

public class IteratorMe {
    public static void main(String[] args) {
        Set s=new HashSet();
        s.add("A");
        s.add("B");
        for (Iterator it =s.iterator();it.hasNext();) {
            String st=(String)it.next();
            System.out.println(st);
        }
    }
}

简单的日历

import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Scanner;

public class RiLi {
    public static void main(String[] args) {
        System.out.println("请输入日期（xxxx-xx-xx）：");
        Scanner sc=new Scanner(System.in);
        String dataString=sc.nextLine();
        String[] str=dataString.split("-");
        int year=new Integer(str[0]);
        int month=new Integer(str[1]);
        int day=new Integer(str[2]);
        Calendar c = new GregorianCalendar(year, month - 1, day);  //转为日历格式
        c.set(Calendar.DATE, 1);  //设置为本月一号
        int maxDate = c.getActualMaximum(Calendar.DATE);//找到本月一共多少天
        if(year>=0&month>=1&month<=12&day>=1&day<=maxDate) {
            int dow = c.get(Calendar.DAY_OF_WEEK); //找到一号是周几
            System.out.println("日\t一\t二\t三\t四\t五\t六");//表头
            for (int i = 0; i < dow - 1; i++) { System.out.print("\t"); }
            for (int i = 1; i <= maxDate; i++) {
                if (i != day) {
                    System.out.print(i + "\t");
                } else {
                    System.out.print(i + "*" + "\t");
                }
                if ((i + dow - 1) % 7 == 0) {  //断行
                    System.out.print("\n");
                }
            }
        }else{
            System.out.println("日期错误");
        }
    }
}