Java Scanner hasNextDouble()方法及示例

java.util.Scanner 类的 hasNextDouble() 方法，如果该扫描器输入的下一个标记可以用nextDouble()方法解释为Double，则返回true。该扫描器不会超过任何输入。

语法

public Double hasNextDouble()

参数： 该函数不接受任何参数。

返回值 ：当且仅当这个扫描器的下一个标记是一个有效的Double时，该函数返回true。

异常 ：如果这个扫描器被关闭，该函数会抛出IllegalStateException。

下面的程序说明了上述函数。

程序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();
    }
}

输出:

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

程序2： 展示例外情况的计划

// 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

**参考资料: ** https://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#hasNextDouble()