Java Scanner hasNextDouble()用法及代碼示例

如果可以使用nextDouble()方法將此掃描儀輸入中的下一個標記解釋為Double，則java.util.Scanner類的hasNextDouble()方法將返回true。掃描儀不會越過任何輸入。

用法:

public Double hasNextDouble()

參數：該函數不接受任何參數。

返回值：僅當此掃描儀的下一個令牌為有效Double時，此函數才返回true。

異常注意：如果關閉此掃描器，則此函數將引發IllegalStateException。

以下示例程序旨在說明上述函數：

示例1:

// Java program to illustrate the 
// hasNextDouble() method of Scanner class in Java 
// without parameter 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) 
        throws Exception 
    { 
  
        String s = "gfg 2 geeks!"; 
  
        // new scanner with the 
        // specified String Object 
        Scanner scanner = new Scanner(s); 
  
        // use US locale to interpret Doubles in a string 
        scanner.useLocale(Locale.US); 
  
        // iterate till end 
        while (scanner.hasNext()) { 
  
            // check if the scanner's 
            // next token is a Double with the default radix 
            System.out.print("" + scanner.hasNextDouble()); 
  
            // print what is scanned 
            System.out.print(" -> " + scanner.next() + "\n"); 
        } 
  
        // close the scanner 
        scanner.close(); 
    } 
}

輸出：

false -> gfg
true -> 2
false -> geeks!

示例2:演示異常的程序

// Java program to illustrate the 
// hasNextDouble() method of Scanner class in Java 
// Exception case 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) 
        throws Exception 
    { 
  
        try { 
            String s = "gfg 2 geeks!"; 
  
            // new scanner with the 
            // specified String Object 
            Scanner scanner = new Scanner(s); 
  
            // use US locale to interpret Doubles in a string 
            scanner.useLocale(Locale.US); 
  
            scanner.close(); 
  
            // iterate till end 
            while (scanner.hasNext()) { 
  
                // check if the scanner's 
                // next token is a Double with the default radix 
                System.out.print("" + scanner.hasNextDouble()); 
  
                // print what is scanned 
                System.out.print(" -> " + scanner.next() + "\n"); 
            } 
  
            // close the scanner 
            scanner.close(); 
        } 
        catch (IllegalStateException e) { 
            System.out.println("Exception: " + e); 
        } 
    } 
}

輸出：

Exception: java.lang.IllegalStateException: Scanner closed

參考： https://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#hasNextDouble()

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