monster-little

java-day02

自增 自减

 //自增 自减
        int a= 3;
        int b =a++;//先打印 再增加
        System.out.println(b);
        int c=++a;//先增加 再打印
        System.out.println(c);

输出 b=3 c=5

幂运算

 //幂运算
        double d = Math.pow(2,3);
        System.out.println(d);

d=8.0

逻辑运算符、位运算符

&& 与

||或

！非

        boolean a = false;
        boolean b = true;
        System.out.println( a&&b);//与 false
        System.out.println(a||b);//或 true

左移<<

右移>>

 System.out.println(2<<3);//0010 左移3位 0001 0000

输出16

字符串连接符

 //字符串连接符   +   ，只要左有string类型
        int a =10 ;
        int b = 20;
        System.out.println(a+b);//30
        System.out.println(""+a+b);//1020
        System.out.println(a+b+"");//30

三元运算符

  //三元运算符 ？ ：
        int a =90;
        String type = a>60?"及格":"不及格";
        System.out.println(type);

输出及格

包机制

JavaDoc

package com.monster.blog.day02;

/**
 * @author monster
 * @version 1.0
 * @since 1.7
 */
public class Doc {
    /**
     *
     * @param name
     * @return
     * @throws Exception
     */
    public  String test(String name)throws Exception{
        return name;

    }

}

Scanner对象

我们可以使用Scanner对象来获取用户的输入

基本语法

Scanner a = new Scanner(System.in);

next()接收

package com.monster.blog.scanner;

import java.util.Scanner;

public class demo01 {
    public static void main(String[] args) {
        //创建一个扫描对象，接受用户信息
        Scanner scanner = new Scanner(System.in);
        System.out.println("使用next方法接收:");
        //判断用户有没有输入字符串
        if (scanner.hasNext()){
            //使用next方法接收
            String str = scanner.next();
            System.out.println("输入内容为"+str);
        }
        scanner.close();
    }
}
//输出hello

nextLine()接收

package com.monster.blog.scanner;
import java.util.Scanner;
public class demo02 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("使用nextline方法接收：");
        if (scanner.hasNextLine()){
            String str = scanner.nextLine();
            System.out.println("输入内容为："+str);
        }
        scanner.close();
    }
}
//输入内容为：hello world

package com.monster.blog.scanner;

import java.util.Scanner;

public class demo03 {
    public static void main(String[] args) {
        int i =0;
        float j = 0.0f;
        System.out.println("请输入一个整数：");
        Scanner scanner = new Scanner(System.in);
        if (scanner.hasNextInt()){
            i = scanner.nextInt();
            System.out.println("输入整数为："+i);
        }else {
            System.out.println("你输入的不是整数");
        }
        System.out.println("请输入一个小数：");
        Scanner scanner1 = new Scanner(System.in);
        if (scanner.hasNextFloat()){
            j = scanner.nextFloat();
            System.out.println("输入小数为："+j);
        }else {
            System.out.println("你输入的不是小数");
        }
        scanner.close();
    }
}


package com.monster.blog.scanner;

import java.util.Scanner;

public class demo04 {
    public static void main(String[] args) {
        //输入几个数，没输入一个数字用回车确认，求总和和平均数
        double sum;
        sum = 0;
        int m =0;
        Scanner scanner = new Scanner(System.in);
        System.out.println("输入数字，回车输入下一个数字，输入其他字符停止：");
        while (scanner.hasNextDouble()){
            double x = scanner.nextDouble();
            m++;
            sum = sum +x;

        }
        System.out.println("总和为："+sum);
        System.out.println("平均值为："+sum/m);
        scanner.close();
    }
}

输入数字，回车输入下一个数字，输入其他字符停止：
1
2
3
4
5
6
sf
总和为：21.0
平均值为：3.5

Process finished with exit code 0

顺序结构

package com.monster.blog.struct;

public class order {
    public static void main(String[] args) {
        System.out.println("hello1");
        System.out.println("hello2");
        System.out.println("hello3");
        System.out.println("hello4");
        System.out.println("hello5");
    }

}

hello1
hello2
hello3
hello4
hello5

Process finished with exit code 0

选择结构

if单选择结构

package com.monster.blog.struct;

import java.util.Scanner;

public class ifdemo01 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入内容：");
        String s = scanner.nextLine();

        if(s.equals("hello")){
            System.out.println(s);
        }
        System.out.println("end");
        scanner.close();
    }
}

请输入内容：
hello
hello
end

Process finished with exit code 0

if双选择结构

package com.monster.blog.struct;

import java.util.Scanner;

public class ifdemo02 {
    public static void main(String[] args) {
        //如果分数大于60 及格，否则不及格
        Scanner scanner = new Scanner(System.in);
        System.out.println("输入成绩：");
        int score = scanner.nextInt();
        if(score<60){
            System.out.println("不及格");
        }else {
            System.out.println("及格");
        }
        scanner.close();
    }
}

输入成绩：
60
及格

Process finished with exit code 0

if多选择结构

package com.monster.blog.struct;

import java.util.Scanner;

public class ifdemo03 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("输入成绩：");
        int score = scanner.nextInt();
        if(score == 100){
            System.out.println("恭喜满分！");
        }else if(score<100&&score>=90){
            System.out.println("获得A");
        }else if(score<90&&score>=80){
            System.out.println("获得B");
        }else if(score<80&&score>=70){
            System.out.println("获得c");
        }else if(score<70&&score>=60){
            System.out.println("获得D");
        }else {
            System.out.println("不及格");
        }

        scanner.close();
    }
}

输入成绩：
79
获得c

Process finished with exit code 0

switch多选择结构

package com.monster.blog.struct;

public class Switchdemo01 {
    public static void main(String[] args) {
        char score ='A';
        switch (score){
            case 'A':
                System.out.println("优秀");
                break;
            case 'B':
                System.out.println("良好");
                break;
            case 'C':
                System.out.println("及格");
                break;
            case 'D':
                System.out.println("加油");
                break;
            case 'E':
                System.out.println("不及格");
                break;
            default:
                System.out.println("未知");
                break;
        }
    }
}

优秀

Process finished with exit code 0

循环结构

while

package com.monster.blog.struct;

public class whiledemo01 {
    public static void main(String[] args) {
        //输出1-10
        int i=0;
        while (i<10){
            i++;
            System.out.println(i);
        }

    }
}

1
2
3
4
5
6
7
8
9
10

Process finished with exit code 0

package com.monster.blog.struct;

public class whiledemo02 {
    public static void main(String[] args) {
        //输出1+2+3+···+10
        int i = 0;
        int sum =0;
        while(i<10){
            i++;
            sum=sum+i;
        }
        System.out.println(sum);
    }
}

55

Process finished with exit code 0

do...while

package com.monster.blog.struct;

public class dowhiledemo03 {
    public static void main(String[] args) {
        //输出1+2+3+···+10
        int i = 0;
        int sum =0;
        do{
            i++;
            sum=sum+i;

        }while (i<10);
        System.out.println(sum);
    }

}

55

Process finished with exit code 0

posted on 2021-04-20 18:43  monster-little  阅读(42)  评论(0)  编辑  收藏  举报

导航