Java 布尔值 Return 错误

Question

我是 java（以及一般编程）的新手，因此决定编写一个程序来检查数字是否为素数。

我制作了一个工作程序：

import java.io.*;

public class PrimeChecker
{
  public static void main (String[] args) throws IOException
  {
    BufferedReader Reader = new BufferedReader (new InputStreamReader (System.in));

    int factor = 2;
    boolean check = true;
    System.out.println("Please input a number.");
    int number = Integer.parseInt(Reader.readLine ());

    if (number == 1)
    {
      System.out.println(number + " is neither prime nor composite.");
    }
    else
    {
      while (factor <= Math.sqrt(number))
      {
        if (number % factor == 0)
        {
          check = false;
          break;
        }
        factor++;
      }
        if (check)
        {
          System.out.println(number + " is a prime number.");
        }
        else
        {
          System.out.println(number + " is a composite number (not prime).");
        }
    }
  }
}

然后我读了 this，决定稍微玩一下布尔值并将其更改为：

import java.io.*;

public class PrimeCheckerv2
{
  public static void main (String[] args) throws IOException
  {
    BufferedReader Reader = new BufferedReader (new InputStreamReader (System.in));

    int factor = 2;
    System.out.println("Please input a number.");
    int number = Integer.parseInt(Reader.readLine ());

    if (number == 1)
    {
      System.out.println(number + " is neither prime nor composite.");
    }
    else
    {
      while (factor <= Math.sqrt(number))
      {
        public boolean isPrime()
        {
          return (!(number % factor == 0));
        }
        factor++;
      }
        if (isPrime)
        {
          System.out.println(number + " is a prime number.");
        }
        else
        {
          System.out.println(number + " is a composite number (not prime).");
        }
    }
  }
}

我相信我按照我阅读的先前链接页面中的指示做了所有事情，但我的新代码出现了这 3 个错误：

File: C:\Users\Aion\Documents\DrJava\Other\PrimeCheckerv2.java  [line: 19]
Error: Syntax error, insert "VariableDeclarators" to complete LocalVariableDeclaration
File: C:\Users\Aion\Documents\DrJava\Other\PrimeCheckerv2.java  [line: 19]
Error: Syntax error, insert ";" to complete BlockStatements
File: C:\Users\Aion\Documents\DrJava\Other\PrimeCheckerv2.java  [line: 19]
Error: Syntax error, insert ";" to complete Statement

我浏览了该网站上的许多问题，寻找可以解释这些问题的内容，但一无所获。谁能告诉我为什么会出现这些错误？

Answer 1

您的代码中有几个错误。

首先你在另一个方法中定义一个新方法。这在 java.

中不起作用

   public boolean isPrime()
    {
      return (!(number % factor == 0));
    }
    factor++;
  }

所以你必须把它放在剩下的代码下面。

其次：该方法必须是静态的，因为您想从静态方法中调用该方法。

第三：你必须将参数传递给方法：

public static boolean isPrime(int number, int factor) {
    return number % factor != 0;
}

你必须调用它：

if (isPrime(factor, number))

所以您的 class 必须如下所示：

public class PrimeCheckerv2 {
    public static void main(String[] args) throws IOException {
        BufferedReader Reader = new BufferedReader(new InputStreamReader(
                System.in));

        int factor = 2;
        System.out.println("Please input a number.");
        int number = Integer.parseInt(Reader.readLine());

        if (number == 1) {
            System.out.println(number + " is neither prime nor composite.");
        } else {
            while (factor <= Math.sqrt(number)) {
                factor++;
                if (isPrime(factor, number)) {
                    System.out.println(number + " is a prime number.");
                } else {
                    System.out.println(number
                            + " is a composite number (not prime).");
                }

            }
        }

    }

    public static boolean isPrime(int number, int factor) {
        return number % factor != 0;
    }

}

Java 布尔值 Return 错误

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