java基础（一）

一、java的安装

下载JDK，安装然后添加环境变量jdk\bin

二、用记事本写第一个java程序

       1、新建Test.java,输入代码

public class Test{public static void main(String[] args){int number = 23;System.out.println(number);  //变量申明并赋值才能使用System.out.println(number);/*多行注释多行注释*/}}

编译：   javac Test.java        然后产生Test.class二进制文件

运行：   java Test

变量命名：以字母、下划线、$开头

变量，取余

public class Test{public static void main(String[] args){int price=499;double weight=12.4;String type="sfddvfv";System.out.println(price);System.out.println(weight);System.out.println("字符串："+weight); //用+连接字符串和数值int a=46;int result=a%7;  //取余}} 

数据类型自动转换：int  + double = double;      char + string = string

接收用户输入Scanner类

import java.util.Scanner;public class Test{public static void main(String[] args){Scanner in = new Scanner(System.in);System.out.println("请输入姓名：");String name = in.next();System.out.println("请输入年龄：");int age = in.nextInt();System.out.println("姓名：" + name);System.out.println("年龄：" + age);}} 

数值交换

public class Test{public static void main(String[] args){int a = 45;int b = 78;int temp = a;a = b;b = temp;System.out.println("a的值为：" + a);System.out.println("b的值为：" + b);}}

boolean类型

public class Test{public static void main(String[] args){int a = 2;int b = 2;boolean flag;flag = (a==b);System.out.println(flag); //ture}}

逻辑运算符： &&     ||    ！

if.....else if.....

import java.util.*;public class Test{public static void main(String[] args){Scanner in = new Scanner(System.in);System.out.println("请输入成绩：");int score = in.nextInt();if (score >= 90){System.out.println("优秀");}else if(score >= 80){System.out.println("良好");}else if(score >= 60){System.out.println("中等");}else{System.out.println("差");}System.out.println("测试");}}

switch

import java.util.*;public class Test{public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.println("请输入名次：");int mingci = input.nextInt();switch(mingci) {case 1:System.out.println("第一名");break;case 2:System.out.println("第二名");break;case 3:System.out.println("第三名");break;default:System.out.println("逐出师门");}}}

判断闰年，平年

import java.util.*;public class Test{public static void main(String[] args){Scanner in = new Scanner(System.in);System.out.println("请输入年份：");int year= in.nextInt();if( year%4==0 && year%100!=0 || year % 400 ==0){System.out.println(year + "是一个闰年");}else{System.out.println(year + "是一个平年");}}}

产生随机数

import java.util.Random;public class Test{public static void main(String[] args){Random x = new Random();int number = x.nextInt(10); //0~9System.out.println("随机数为：" + number);int a = (int)(Math.random()*10);System.out.println("随机数为：" + a);}}