[Java知识库]java基础题目练习（持续添加）

控制语句

1、打印九九乘法表

public class work01 {
    public static void main(String[] args){
        for (int i = 1;i < 10;i++){
            for (int j = 1;j <= i;j++){
                if((i == 3 && j == 3) || (i == 4 && j == 3)){
                    System.out.print(" ");
                }
                System.out.print(j + "x" + i + "=" + (j*i) + "  ");
            }
            System.out.println();
        }
    }
}

代码实现：

2、打印三角形

public class work02 {
    public static void main(String[] args){
        for(int i = 1;i<= 4;i++){
            for(int j = 1;j<=(4-i);j++){
                System.out.print(" ");
            }
            for (int j = 1;j<=(i*2-1);j++){
                System.out.print("*");
            }
            System.out.println();
        }
    }
}

代码实现：

3、打印菱形

public class work03 {
    public static void main(String[] args) {
        for(int i = 1;i<= 4;i++){
            for (int j = 1;j<= 4-i;j++){
                System.out.print(" ");
            }
            for (int j = 1;j<=(i*2-1);j++){
                System.out.print("*");
            }
            System.out.println();
        }
        for(int i = 1;i<= 3;i++){
            for (int j = 3;j>(3-i);j--){
                System.out.print(" ");
            }
            for (int j = 5;j>=(i*2-1);j--){
                System.out.print("*");
            }
            System.out.println();
        }

    }
}

代码实现：

4、打印空心菱形

public class work04 {
    public static void main(String[] args) {
        for(int i = 1;i<= 4;i++){
            for (int j = 1;j<= 4-i;j++){
                System.out.print(" ");
            }
            for (int j = 1;j<=(i*2-1);j++){
                if(j==1|| j==(i*2-1) ) {
                    System.out.print("*");
                }else {
                    System.out.print(" ");
                }
            }
            System.out.println();
        }
        for(int i = 1;i<= 3;i++){
            for (int j = 3;j>(3-i);j--){
                System.out.print(" ");
            }
            for (int j = 5;j>=(i*2-1);j--){
                if(j==5 || j==(i*2-1)) {
                    System.out.print("*");
                }else{
                    System.out.print(" ");
                }
            }
            System.out.println();
        }
    }
}
代码实现：

5、已知账号admin，密码123456，使用键盘录入账号密码完成登录验证流程，允许输错三次，三次后提示账号锁定

方法一：
import java.util.Scanner;

public class work05 {
    public static void main(String[] args) {
        final String STR  = "admin";
        final int RESULT  = 123456;
        Scanner scanner = new Scanner(System.in);
        String str;
        int result;
        int num = 2;
        for(;;){
            System.out.print("请输入账号：");
            str = scanner.next();
            System.out.print("请输入密码：");
            result = scanner.nextInt();
            if(str.equals(STR) && RESULT == result){
                System.out.println("登录成功，欢迎回来！！！");
                break ;
            }else{
                if (num == 0){
                    System.out.println("因错误次数过多，您的账户已经被锁定！");
                    break;
                }
                System.out.println("您的输入有误，请重新输入：你还有" + num + "次机会！！！");
                num--;
            }
        }
    }
}

方法二：

import java.util.Scanner;

public class work05 {
    public static void main(String[] args) {
        int RESULT = 123456;
        String STR = "admin";
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入账号：");
        String str = scanner.next();
        System.out.print("请输入密码：");
        int result = scanner.nextInt();
        for (int i = 2;i> 0;i--){
            if((!STR.equals(str)) || (!(RESULT == result))){
                System.out.println("您输入的信息有误，请重新输入，你还有" + i + "次机会" );
            }else {
                System.out.println("登录成功，欢迎回来！！！");
                break;
            }
            System.out.print("请输入账号：");
            str = scanner.next();
            System.out.print("请输入密码：");
            result = scanner.nextInt();
        }
    }
}

代码实现：

6、随机生成一个1~100整数，然后输入一个整数和生成的数字进行比对，猜大小并给予提示，猜对为止。

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

public class work06 {
    public static void main(String[] args) {
        Random random = new Random();
        int result = (random.nextInt(99) + 1);
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入一个 0  --  100 的数字:");
        int sum = scanner.nextInt();
        for(;;){
            if(sum > result){
                System.out.println("猜错了，不妨往小一点试试");
                System.out.print("请重新输入一个 0  --  100 的数字:");
                sum = scanner.nextInt();
            }else if(sum < result){
                System.out.println("猜错了，不妨往大一点试试");
                System.out.print("请重新输入一个 0  --  100 的数字:");
                sum = scanner.nextInt();
            }else if(sum == result){
                System.out.println("恭喜你，猜对了");
                break;
            }
        }
        System.out.println("您的幸运数字为：  " + result);
    }
}

代码实现：

7、由键盘输入一个4位整数，求将该数反转以后的数，如原数为1234，反转后的数位4321

import java.util.Scanner;

public class work07 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入一个四位数的整数：");
        int num = scanner.nextInt();
        int temp = 0;
        System.out.print("反转：");
        for (;;){
            if(num == 0){
                break;
            }
            temp = num%10;
            System.out.print(temp);
            num /= 10;
        }
    }
}

代码实现：

8、int a = 2; int b = 5;如何不使用第三个变量交换两个数？(不可以使用按位运算)

public class work08 {
    public static void main(String[] args) {
        int a = 2;
        int b = 5;
//        a *=b;
//        b = a/b;
//        a /=b;
        a = a+b;
        b = a-b;
        a = a-b;
        System.out.println("a = " + a);
        System.out.println("b = " + b);
    }
}
代码实现：

9、输入一个整数，计算该数有多少位，例如123有3位

import java.util.Scanner;

public class work09 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入一个正整数：");
        int result = scanner.nextInt();
        int temp = 1;
        for (;;){
            if(result/10 == 0 ){
                System.out.println("您输入的是一个" + temp + "位数！");
                break;
            }
            result /= 10;
            temp++;
        }
    }
}

代码实现：