Java中的 Scanner hasNextDouble() 方法及示例

如果可以使用 nextDouble() 方法将此扫描器输入中的下一个标记解释为 Double，则Java.util.Scanner类的hasNextDouble()方法返回 true。扫描仪不会超过任何输入。

句法：

public Double hasNextDouble()

参数：该函数不接受任何参数。

返回值：当且仅当此扫描器的下一个标记是有效的 Double 时，此函数才返回 true。

异常：如果此扫描仪关闭，该函数将抛出IllegalStateException 。

下面的程序说明了上述函数：

方案一：

// 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();
    }
}

输出：

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

程序 2：演示异常的程序

// 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);
        }
    }
}

输出：

Exception: java.lang.IllegalStateException: Scanner closed

参考： https: Java/util/Scanner.html#hasNextDouble()