java编程入门一

学习视频传送门

1.helloword

1.1 println

public class helloWorld {
    public static void main (String[] args){
        System.out.println("hello world tom");
    }
}

1.2  myOneJava.java

public class myOneJava{
    public static void main(String[] args){
        System.out.println("Today is sunday");
    }
}

2.三元运算符

2.1 三个和尚

public class heshang{
    public static void main (String[] args){
        int height1 = 150;
        int height2 = 210;
        int height3 = 165;
        
        int temHeight = (height1>height2) ? height1 :height2;
        int max = (temHeight>height3) ? temHeight : height3;
        
        System.out.println("maxHeight:" + max);
    }
}

2.2 两只老虎

public class twoTiger{
    public static void main (String[] args){
        int weight1 = 180;
        int weight2 = 200;
        // a>b?a:b;
        boolean b = (weight1 == weight2)? true:false;
        System.out.println("b:" + b);
        
    }
}

3. 数据输入

3.1 数据输入

import java.util.Scanner;
public class inputDate{
    public static void main (String[] args){
        System.out.println("Input what?please:");
        Scanner sc = new Scanner(System.in);
        int i = sc.nextInt();
        System.out.println("output : " + i);
    }
}

3.2三个和尚升级版

import java.util.Scanner;

public class heShangMax{
    public static void main (String[] args){
    Scanner sc = new Scanner(System.in);
    
    System.out.println("please input 1 heshang:");
    int height1 = sc.nextInt();
    System.out.println("please input 2 heshang:");
    int height2 = sc.nextInt();
    System.out.println("please input 3 heshang:");
    int height3 = sc.nextInt();
    
    int temHeight = (height1 > height2)?height1:height2;
    int maxHeight = (temHeight > height3)?temHeight:height3;
    
    System.out.println("max height is : "+maxHeight);
    }
}

4.IF语句

4.1  if

public class ifLearn{
    public static void main(String[] args){
        int a = 10;
        int b = 20;
        if (a > b){
            System.out.println("a>b");
        } else if(a < b){
            System.out.println("a < b");
        } else{
            System.out.println("a = b");
        }
    }
}

4.2 奇偶数

import java.util.Scanner;

public class jioushu{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        System.out.println("please input a number:");
        int number = sc.nextInt();
        
        if (number%2 == 0){
            System.out.println(number + " is jishu");
        }else {
            System.out.println(number + " is oushu");
        }
    }
}

4.3 考试奖励

import java.util.Scanner;
public class kaoshijiangli{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        System.out.println("input you score: ");
        int score = sc.nextInt();
        if (score >=80 && score <= 100){
            System.out.println("very good!");
        }else if (score >=60 && score <80){
            System.out.println("just so so");
        }else if (score >=0 && score < 60){
            System.out.println("son of bitch !");
        }else{
            System.out.println("Input score in \"0-100\" please !");
        }
    }
}

5. Switch

5.1 Demo

import java.util.Scanner;

public class SwitchDemo{
    public static void main(String[] args){
        System.out.println("请输入个数字吧:");
        Scanner sc = new Scanner(System.in);
        
        int week = sc.nextInt();
        switch (week){
            case 1:
                System.out.println("星期一");
                break;
            case 2:
                System.out.println("星期二");
                break;
            case 3:
                System.out.println("星期三");
                break;            
            case 4:
                System.out.println("星期四");
                break;    
            case 5:
                System.out.println("星期五");
                break;    
            case 6:
                System.out.println("星期六");
                break;    
            case 7:
                System.out.println("星期日");
                break;    
            default:
                System.out.println("请输入数字1-7之间");
        }
        
    }
}

5.2 四季

import java.util.Scanner;

public class SiJi{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        
        System.out.println("请输入一个月份：1-12之间");
        
        int month = sc.nextInt();
        switch (month){
            case 3,4,5:
            System.out.println("春暖花开");
            break;
            case 6,7,8:
            System.out.println("夏果累累");
            break;
            case 9,10,11:
            System.out.println("秋风萧瑟");
            break;    
            case 12,1,2:
            System.out.println("冬雪皑皑");
            break;
            default:
            System.out.println("请输入月份在1-12之间");
        }
    }
}

6. For 循环

6.1 Demo

/*
格式：
for (初始化语句;条件判断语句;条件控制语句){
    循环体语句;
}

执行流程1.执行初始化语句2. 执行条件判断语句3.执行循环体语句。4.执行条件控制语句 5.回到二继续执行
*/
public class ForDemo{
    public static void main(String[] args){
        for (int i=0;i<5;i++){
            System.out.println("HELLOWORD");
        }
        for (int n=1;n<=5;n++){
            System.out.println(n);
        }
        for (int i=5;i>=1;i--){
            System.out.println(i);
        }
    }
}

6.2 求和

public class ForSum{
    public static void main(String[] args){
        int sum =0;
        int sum1=0;
        for(int i=1;i<=100;i++){
            sum += i;
        }
        System.out.println(sum);
        System.out.println("-----------(づ￣3￣)づ╭❤～求偶数和--------------");
        
        for (int j=1;j<=100;j++){
            if (j%2==0){
                sum1 +=j;
            }
        }System.out.println(sum1);
    }
}

6.3 水仙花与计数

//在控制台输出水仙花数
public class shuixianhuashu{
    public static void main(String[] args){
        int count = 0;
        for (int i=100;i<=999;i++){
            //在计算前获取三位数中每个位上的值
            int ge =i%10;
            int shi = i/10%10;
            int bai = i/100%10;
            
            //判定条件是将三位数中的每个数值取出来，计算立方和后与原数相同
            if(ge*ge*ge+shi*shi*shi+bai*bai*bai ==i){
                //计数count
                count++;
                System.out.println(i);
            }
        }System.out.println("水仙花数"+count+"个");
    }
}

7. while 循环

 7.1 Demo

public class whileDemo{
    public static void main(String[] args){
        //在控制台输出10次helloword
        int i = 0;
        while (i<=10){
            System.out.println("helloword");
            i++;
        }
    }
}

7.2 折纸珠穆朗玛峰

public class zhumulangmafeng{
    public static void main(String[] args){
        double paper = 0.1;
        int zf = 8844430;
        int count = 0;
        while (paper <= zf){
            paper *=2;
            count++;
        }
        System.out.println("一张纸需要折叠"+count+"次，才等于珠穆朗玛峰高度");
    }
}

7.3 do..while

/* 完整格式
do {
    循环体语句;
    条件控制语句;
}while(条件判断语句);

*/

public class doWhileDemo{
    public static void main(String[] args){
        int i = 0;
        do{
            System.out.println(i);
            i++;
        }while (i<=5);
    }
}

7.4 continue & break 循环控制

public class conBreak{
    public static void main(String[] args){
        for (int i=1;i<=5;i++){
            if(i%2 == 0){
                //continue;
                break;
            }
            
            System.out.println(i);
        }
    }
}

8. Random

 8.1 Demo

import java.util.Random;

public class randomDemo{
    public static void main(String[] args){
        Random r = new Random();
        int number = r.nextInt(10);
        
        System.out.println(number);
    }
}

8.2 猜数字

import java.util.Random;
import java.util.Scanner;

public class caishuzi{
    public static void main(String[] args){
    Random r = new Random();
    int number = r.nextInt(100)+1;
    while (true){
        Scanner sc = new Scanner(System.in);
        int InNumber = sc.nextInt();
        if (InNumber > number){
            System.out.println("大了");
        }else if (InNumber < number){
            System.out.println("小了");
        }else{
            System.out.println("猜对了，正是："+InNumber);
            break;
        }    
    } 

    }
}

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