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Java学习笔记 - 基础入门(一)

copylian    0 评论    8143 浏览    2023.06.04

Java 是一个通用术语,用于表示 Java 软件及其组件,包括“Java 运行时环境 (JRE)”、“Java 虚拟机 (JVM)”以及“插件”。 Java具有大部分编程语言所共有的一些特征,被特意设计用于互联网的分布式环境。Java具有类似于C++语言的形式和感觉,但它要比C++语言更易于使用,而且在编程时彻底采用了一种以对象为导向的方式。

教程:https://www.bilibili.com/video/BV1rB4y1G7WE

Java下载https://www.oracle.com/java/technologies/downloads/#jdk20-windows

Java IDE IntelliJ:https://www.jetbrains.com.cn/idea/download/#section=windows

环境配置:

        添加环境变量:path 下添加java的bin目录 C:\Program Files\Java\jdk1.8.0_361\bin

        添加常量:JAVA_HOME:C:\Program Files\Java\jdk1.8.0_361

查看版本:java -version

java version "1.8.0_361"

Java(TM) SE Runtime Environment (build 1.8.0_361-b09)

Java HotSpot(TM) 64-Bit Server VM (build 25.361-b09, mixed mode)

一、基础

1)、二进制转十进制:0 0 0 0 1 1 1 1 = 0 + 0 + 0 + 0 + 1(8) + 1(4) + 1(2) + 1(1) = 15

2)、十进制转二级制:15转二级制

        15/2 = 7 余数 1

        7/2 = 3 余数 1

        3/2 = 1 余数 1

        1/2 = 0 余数 1

        结果:0 0 0 0 1 1 1 1

3)、数据类型:

微信图片_20230604222920.png

4)、数组:

int[] scores = {1,2,3,4,5};

int[] scores = new int[3];

scores[0] = 1;

scores[1] = 2;

scores[2] = 3;

System.out.println("scores = " + Arrays.toString(scores));


//定义

int[] scores = new int[5];


//系统输入

Scanner scanner = new Scanner(System.in);

for (int i = 0; i < 5; i++) {

        scores[i] = scanner.nextInt();

}


//排序

Arrays.sort(scores);

System.out.println("scores = " + Arrays.toString(scores));


5)、类、字符串、随机数、递归、正则表达式:

package copylian.java;

import java.util.Arrays;

import java.util.Random;

import java.util.Scanner;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class Student {

        //属性

        String stdName;

        int age;

        String[] course;


        /**

        * 获取学生信息

        * @author copylian@aikehou.com

        * @date 2023年6月4日23:20:14

        * @return String[]

        */

        private String getStdName(){

                return "学生:" + stdName + " , 年龄:" + age + " 岁, 学习了课程:" + Arrays.toString(course);

        }


        /**

        * 获取学生其他信息

        * @author copylian@aikehou.com

        * @date 2023年6月4日23:20:14

        * @return String[]

        */

        public String[] getCourse(){

                String info = getStdName();

                String[] arr = new String[]{info, "其他信息"};

                return arr;

        }


        /**

        * 递归

        * @param num

        * @return

        */

        public static int digui(int num){

                if (num == 1){

                        return num;

                } else {

                        return num * digui(num - 1);

                }

        }


        /**

        * main

        * @param args

        */

        public static void main(String[] args){

                //实例化

                Student student = new Student();

                student.stdName = "只袄早";

                student.age = 20;

                student.course = new String[]{"GoLnag","PHP","Python","Java"};

                String info = student.getStdName();System.out.println("info = " + info);

                

                String[] other  = student.getCourse();

                System.out.println("Arrays.toString(other) = " + Arrays.toString(other));

                

                //字符、字符串:

                char a = 'A'; // 字符只能是一个

                String b = "ABCD";

                System.out.println("a = " + a);

                System.out.println("b = " + b);

                System.out.println("b.equals(a) = " + b.equals(a));

                

                //字符串操作

                b.concat();

                b.trim();

                b.split();

                b.substring();

                b.indexOf();

                b.lastIndexOf();

                

                //StringBuffer() - 多线程、StringBuilder() - 单线程

                Scanner input = new Scanner(System.in);

                String str = input.next();


                StringBuffer strbuf = new StringBuffer(str);

                System.out.println("strbuf = " + strbuf);


                strbuf.append("Java"); // 附加

                System.out.println("strbuf = " + strbuf);


                strbuf.insert(0,"aaa"); // 插入

                System.out.println("strbuf = " + strbuf);

                

                //随机数

                double math = Math.random();

                System.out.println("math = " + math); // 很短时间内可能出现重复

                

                Random r = new Random();

                Double r1 = r.nextDouble();

                System.out.println("r1 = " + r1);

                

                int r2 = r.nextInt(100);

                System.out.println("r2 = " + r2);

                

                //递归

                int dg = digui(5);

                System.out.println("dg = " + dg);

                

                //正则表达式

                String regex = "^1[345789]\\d{9}";

                Pattern p = Pattern.compile(regex);

                Matcher m = p.matcher("15859279220");

                System.out.println("m.matches() = " + m.matches());

                System.out.println("m.find() = " + m.find());

                while(m.find()){

                        System.out.println("m.group() = " + m.group()); // m.group() 获取匹配的字序列

                }

        }

}


6)、Java OOP封装:封装、继承(extends)、多态、抽象类(abstract)、接口类(interface),接口类继承(implements),基本上跟PHP的类似,这里就不详细赘述了

import copylian.java.oop.Animal;

import java.util.Arrays;

public class Testoop {

        public static void  main(String[] args){

                String type = "狗东西";

                int age = 10;

                String[] hobbys = new String[]{"抓老鼠","出去玩"};

                Animal animal = new Animal(type, age, hobbys);

                System.out.println("animal = " + animal.getType() + animal.getAge() + Arrays.toString(animal.getHobbys()));

        }

}


//Animal.java类

package copylian.java.oop;

import copylian.java.Student;

public class Animal extends Student {

        //类型

        private String type;


        //age

        public int age;


        //爱好

        protected String[] hobbys;


        //颜色

        public static String color;


        /**

        * 构造函数:可以同时存在多个同名的构造函数,但是参数得不一样

        * @param type

        * @param age

        * @param hobbys

        */

        public Animal(String type, int age, String[] hobbys) {

                //super父类

                super();

                this.type = type;

                this.age = age;

                this.hobbys = hobbys;

        }

        

        /**

        * 同名构造方法

        * @param type

        * @param age

        */

        public Animal(String type, int age) {

                this.type = type;

                this.age = age;

        }

        

        /**

        * 静态方法:不能访问非静态属性

        */

        public static void print(){

                System.out.println("color = " + color);

        }

        

        public String getType() {

                return type;

        }

        

        public void setType(String type) {

                this.type = type;

        }

        

        public int getAge() {

                return age;

        }

        

        public void setAge(int age) {

                this.age = age;

        }

        

        public String[] getHobbys() {

                return hobbys;

        }

        

        public void setHobbys(String[] hobbys) {

                this.hobbys = hobbys;

        }

}



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