使用Scanner在簡單Java程序中編譯錯誤

Question

import java.util.*;
public class strings {
    public static void main (String [] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Type your first integer: ");
        int first = keyboard.next();
        System.out.print("Type your seconds integer : ");
        int second = keyboard.next();
        System.out.print("The sum of your two integers are:");
    }
}

我不知道為什么我在字符串上得到2個錯誤無法轉換為int。

Answer 1

keyboard.nextInt(); 

代替

keyboard.next();

如果你想使用keyboard.next(); ，然后int first將int first更改為String first 。

將代碼修改為：

import java.util.*;
public class Demo {
    public static void main (String [] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Type your first integer: ");
        int first = keyboard.nextInt();

        System.out.print("Type your seconds integer : ");
        int second = keyboard.nextInt();

        System.out.print("The sum of your two integers are:" +(first+second));
    }
}

將您的類名更改為另一個而不是string 。

Answer 2

有多種方法可以執行此操作，具體取決於您要執行的驗證量。

在下面的解決方案中，使用.nextInt（）獲得第一個數字。 注意，如果它不是整數，我們需要清除流輸入，所以在捕獲InputMismatchException時我們會調用.next（）。 否則，由於尚未清除輸入，因此將繼續發生相同的異常

第二個數字是使用.next（）獲得的，它返回一個字符串，然后我們將該字符串轉換為整數。 請注意，這里我們捕獲一個不同的異常NumberFormatException以確保輸入仍然良好。 （我們不會調用.next（））

 public static void main (String [] args) {
    try (Scanner keyboard = new Scanner(System.in)) {
        System.out.print("Type your first integer: ");
        int first;
        do {
            try {
                first = keyboard.nextInt();
                break;
            } catch (InputMismatchException e) {
                keyboard.next();
                System.out.print("Invalid first integer, try again: ");
            }
        } while (true);
        System.out.print("Type your seconds integer : ");
        int second;
        do {
            try {
                second = Integer.valueOf(keyboard.next());
                break;
            } catch (NumberFormatException e) {
                System.out.print("Invalid seconds integer, try again: ");
            }
        } while (true);
        System.out.print("The sum of your two integers are: " + (first + second));
    }
}

我做的最后一件事是嘗試使用資源，這樣輸入流將被關閉，無論程序是否正常退出或拋出異常。

Answer 3

Scanner類next()方法返回String值。 您可以執行以下任何步驟來解決編譯錯誤。

1. 您需要將String值轉換為int。

    int first = Integer.parseInt(keyboard.next()); 

2. 您可以使用nextInt()方法直接從用戶獲取int值。

Answer 4

這將讀取整行，然后將其轉換為整數

int first = Integer.paresInt（keyboard.nextLine（））;

要么

如果您確定輸入數字

int first = keyboard.nextInt（）;

Answer 5

我有三個解決這個問題的方法：

第一

在您的代碼中，您使用的是keyboard.next() ，它將返回一個您必須將其轉換為Integer的字符串。 為此您可以使用keyboard.nextInt() ，它將直接將字符串轉換為整數。

import java.util.Scanner;

public class strings {
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Type your first integer: ");
        int first = keyboard.nextInt();
        System.out.print("Type your seconds integer : ");
        int second = keyboard.nextInt();
        System.out.print("The sum of your two integers are:"+(first+second));
    }
}

第二

或者你可以使用Integer.parseInt(**String to be converted to Integer**)將string into Integer Integer.parseInt(**String to be converted to Integer**) ，這會將string into Integer 。

import java.util.Scanner;

public class strings {
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Type your first integer: ");
        int first = Integer.parseInt(keyboard.next());
        System.out.print("Type your seconds integer : ");
        int second = Integer.parseInt(keyboard.next());
        System.out.print("The sum of your two integers are:"+(first+second));
    }
}

第三

或者你可以使用Integer.valueOf(**String to be converted to Integer**)將string into Integer Integer.valueOf(**String to be converted to Integer**) ，這會將string into Integer 。

import java.util.Scanner;

public class strings {
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Type your first integer: ");
        int first = Integer.valueOf(keyboard.next());
        System.out.print("Type your seconds integer : ");
        int second = Integer.valueOf(keyboard.next());
        System.out.print("The sum of your two integers are:"+(first+second));
    }
}

Answer 6

您可以使用scanner.nextLine() （讀取輸入直到行的末尾），它給出String輸出並使用Integer.parseInt將其轉換為int ，如下所示：

          Scanner keyboard = new Scanner(System.in);
          try {
              System.out.print("Type your first integer: ");
              int first = Integer.parseInt(keyboard.nextLine());
              System.out.print("Type your seconds integer : ");
              int second = Integer.parseInt(keyboard.nextLine());
              int sum  =first+second;
              System.out.print("The sum of your two integers are:"+sum);
          } catch(Exception exe) {
              System.out.println(" Error!!!! Please try again !!!! ");
          } finally {
              keyboard.close();
          }

此外，嘗試close資源（在finally塊中，如上所示）作為練習。

Answer 7

您正在使用Scanner類中的next（）方法。 此方法返回String，您不能將字符串存儲在int類型變量中。 因此，您可以對int類型輸入使用nextInt（）方法，或者您可以將值存儲在String變量中，之后可以將String變量轉換為int。

請遵循以下代碼：

import java.util.*;
public class strings {
    public static void main (String [] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Type your first integer: ");
        int first = keyboard.nextInt();
        System.out.print("Type your seconds integer : ");
        int second = keyboard.nextInt();
        System.out.print("The sum of your two integers are:" +(first+second));
    }
}

或遵循此代碼

import java.util.*;
public class strings {
    public static void main (String [] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Type your first integer: ");
        //Get String input and stroe at String variable
        String firstString = keyboard.next();
        //Convert the String variable to int 
        int first=Integer.parseInt(firstString);
        System.out.print("Type your seconds integer : ");
        //Get String input and stroe at String variable
        String secondString = keyboard.next();
        //Convert the String variable to int 
        int second=Integer.parseInt(secondString);
        System.out.print("The sum of your two integers are:" +(first+second));
    }
}

Answer 8

正如其他人所說，你可以使用

int first = keyboard.nextInt();

但你也可以使用next（）方法和parseInt，如果你願意，可以有一個顯示錯誤信息的便利。

import java.util.*;
public class myClass {
public static void main (String [] args) {
    Scanner keyboard = new Scanner(System.in);
    System.out.println("Type your first integer: ");
    String firstStr = keyboard.next();
    System.out.println("Type your seconds integer : ");
    String secondStr = keyboard.next();
    int first = -1; //assuming only positive integers
    int second = -1;
     do{
      try{
      first = Integer.parseInt(firstStr);
      second = Integer.parseInt(secondStr);
      int sum = first + second;
      System.out.println("The sum of your two integers are: " + sum);
     } catch (NumberFormatException exception) {
      System.out.println("Integers only.");
     }
  } while (first=-1 && second=-1);
 }
}

Answer 9

更改您的first和second變量

int first = keyboard.next();  
int second = keyboard.next();

至

int first = keyboard.nextInt();
int second = keyboard.nextInt();

Answer 10

你應該用nextInt替換next，就像這樣

int first = keyboard.nextInt();

從API中，您可以看到next的返回類型是String，而nextInt（）是int。

Answer 11

問題在這里：

int first = keyboard.next();

Scanner.next返回String，你期望int，所以你需要替換它

int first = keyboard.nextInt();

同樣

  int second = keyboard.nextInt();

Answer 12

嘗試使用

keyboard.nextInt();

不

keyboard.next();

它顯示它無法轉換，因為.next用於字符串，但對於其他數據類型是.next，然后是帶有大寫的數據類型。 例如：

long l=keyboard.nextLong(); 

和boolean b=keyboard.nextBoolean();

Answer 13

keyboard.next（）將從掃描程序返回下一個完整的令牌，我想到字符串類型所以需要將其轉換為整數，更好的選擇是使用keyboard.nextInt（）方法獲取整數輸入。

Answer 14

你已經將代碼更改為：

import java.util.*;
public class strings {
    public static void main (String [] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Type your first integer: ");
        int first = keyboard.nextInt();
        System.out.println("Type your seconds integer : ");
        int second = keyboard.nextInt();
        System.out.print("The sum of your two integers are:"+(first+second));
    }
}