Java 算法基础：输入输出与格式化实战 | 极客日志

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Java 算法基础：输入输出与格式化实战

综述由AI生成Java 算法基础题涵盖输入输出处理、字符串格式化、进制转换及几何计算。通过 Scanner 类读取数据，利用 String.format 控制输出格式，掌握 %s、%d、%f 等占位符用法。涉及整数逆序、多项式求值、圆与椭圆面积周长计算等常见逻辑。代码示例修正了语法细节，适合初学者巩固 Java 基础语法与基本算法思维。

ArchDesign发布于 2026/3/15更新于 2026/4/251 浏览

Java 算法基础：输入输出与格式化实战

在 Java 算法入门阶段，掌握基础的输入输出处理与格式化技巧是构建后续逻辑的基石。本文整理了 13 道经典基础题，涵盖字符串截取、格式控制、进制转换及几何计算等常见场景。代码已修正语法细节，适合初学者巩固基础。

1. 输入宽度与字符串截取

读取一个连续字符串并按固定长度分割输出。这里主要考察 Scanner 的使用以及字符串子串操作。

package demo5_2;
import java.util.Scanner;

public class Main10 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String all = sc.next();
        System.out.println(String.format("%d %d %d",
                Integer.parseInt(all.substring(0, 3)),
                Integer.parseInt(all.substring(3, 6)),
                Integer.parseInt(all.substring(6, 9))));
        sc.close();
    }
}

注意 substring 的索引范围，前闭后开，确保不越界。

2. 字符串占位符 `%s`

输入字符串并输出前 3 个字符，要求右对齐且占用 6 列宽。这涉及 String.format 的宽度控制。

package demo5_2;
import java.util.Scanner;

public class Main11 {
    public static void main(String[] args) {
        Scanner sc = new (System.in);
           sc.nextLine();
        System.out.println(String.format(, c.substring(, )));
    }
}

package demo5_2;
import java.util.Scanner;

public class Main12 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        System.out.println(String.format("%f", a) + " " +
                String.format("%.2f", a) + " " +
                String.format("%8.3f", a));
    }
}

package demo5_2;

public class Main13 {
    public static void main(String[] args) {
        double n = 3.1415926;
        double m = 12345678.123456789;
        // 小数形式保留 6 位，指数形式配合调整
        System.out.printf("%.6f %.6fe+000\n", n, n);
        System.out.printf("%.6f %.6fe+007\n", m, m / 10000000);
    }
}

package demo5_2;

public class Main {
    public static void main(String[] args) {
        int a = 202, b = 117, c = 70, d = 130;
        // 输出格式要求前缀为 0 或 0X
        System.out.printf("%d 0%o 0X%X\n", a, a, a);
        System.out.printf("%d 0%o 0X%X\n", b, b, b);
        System.out.printf("%d 0%o 0X%X\n", c, c, c);
        System.out.printf("%d 0%o 0X%X\n", d, d, d);
    }
}

package demo5_2;
import java.util.Scanner;

public class Main15 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String c = sc.nextLine().replace(" ", "");
        System.out.println(Integer.valueOf(c));
        sc.close();
    }
}

package demo5_2;
import java.util.Scanner;

public class Main16 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        // 方法一：数学运算
        // int a = sc.nextInt();
        // System.out.print(a % 10);
        // System.out.print(a / 10);

        // 方法二：字符串反转
        StringBuilder sb = new StringBuilder();
        String str = sc.next();
        sb.append(str).reverse();
        System.out.println(sb);
    }
}

package demo5_2;
import java.util.Scanner;

public class Main17 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int x = sc.nextInt();
        // 注意 Math.pow 结果为 double，需强制类型转换
        System.out.println((int) (Math.pow(x, 6) + 3 * Math.pow(x, 4)
                - 2 * Math.pow(x, 5) - 5 * Math.pow(x, 2) + 6 * x + 7));
    }
}

package demo5_2;
import java.util.Scanner;

public class Main18 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int x = sc.nextInt();
        int y = sc.nextInt();
        System.out.println((x + y) * (x + y) * (x + y));
    }
}

package demo5_2;
import java.util.Scanner;

public class Main19 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        System.out.println(String.format("%.6f", Math.abs(a)));
    }
}

package demo5_2;
import java.util.Scanner;

public class Main20 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double r = sc.nextDouble();
        double PI = 3.1415926;
        double Circumference = 2 * PI * r;
        double Area = PI * r * r;
        System.out.println("Area=" + String.format("%.6f", Area));
        System.out.println("Circumference=" + String.format("%.6f", Circumference));
    }
}

package demo5_2;
import java.util.Scanner;

public class Main21 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double x = sc.nextDouble();
        double y = sc.nextDouble();
        double Area = x * y;
        double Perimeter = 2 * (x + y);
        System.out.println("Area=" + String.format("%.6f", Area));
        System.out.println("Perimeter=" + String.format("%.6f", Perimeter));
    }
}

package demo5_2;
import java.util.Scanner;

public class Main22 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        double PI = 3.1415926;
        double Area = PI * a * b;
        System.out.println("Area" + " " + "=" + " " + String.format("%.6f", Area));
    }
}