Java Scanner nextDouble()方法及示例

java.util.Scanner 类的 nextDouble() 方法将输入的下一个标记扫描为Double。如果翻译成功，扫描器就会前进到匹配的输入。

语法

public double nextDouble()

参数： 该函数不接受任何参数。

返回值： 该函数返回从输入的 Double扫描 值。

异常： 该函数会抛出三种异常，如下所述。

• InputMismatchException： 如果下一个标记与Double正则表达式不匹配，或者超出了范围。
• NoSuchElementException： 如果输入已经用完，则抛出。
• IllegalStateException： 如果该扫描器被关闭，则抛出。

下面的程序说明了上述功能。

程序1 :

// Java program to illustrate the
// nextDouble() 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 9 + 6 = 12.0";
  
        // create a new scanner
        // with the specified String Object
        Scanner scanner = new Scanner(s);
  
        while (scanner.hasNext()) {
  
            // if the next is a Double,
            // print found and the Double
            if (scanner.hasNextDouble()) {
                System.out.println("Found Double value :"
                                   + scanner.nextDouble());
            }
  
            // if no Double is found,
            // print "Not Found:" and the token
            else {
                System.out.println("Not found Double() value :"
                                   + scanner.next());
            }
        }
        scanner.close();
    }
}

输出:

Not found Double() value :Gfg
Found Double value :9.0
Not found Double() value :+
Found Double value :6.0
Not found Double() value :=
Found Double value :12.0

程序2： 演示InputMismatchException

// Java program to illustrate the
// nextDouble() method of Scanner class in Java
// InputMismatchException
  
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
  
        try {
  
            String s = "Gfg 9 + 6 = 12.0";
  
            // create a new scanner
            // with the specified String Object
            Scanner scanner = new Scanner(s);
  
            while (scanner.hasNext()) {
  
                // if the next is a Double
                // print found and the Double
                // since the value 60 is out of range
                // it throws an exception
  
                System.out.println("Next Double value :"
                                   + scanner.nextDouble());
            }
            scanner.close();
        }
        catch (Exception e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

输出:

Exception thrown: java.util.InputMismatchException

程序3： 演示NoSuchElementException

// Java program to illustrate the
// nextDouble() method of Scanner class in Java
// NoSuchElementException
  
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
  
        try {
  
            String s = "Gfg";
  
            // create a new scanner
            // with the specified String Object
            Scanner scanner = new Scanner(s);
  
            // Trying to get the next Double value
            // more times than the scanner
            // Hence it will throw exception
            for (int i = 0; i < 5; i++) {
  
                // if the next is a Double,
                // print found and the Double
                if (scanner.hasNextDouble()) {
                    System.out.println("Found Double value :"
                                       + scanner.nextDouble());
                }
  
                // if no Double is found,
                // print "Not Found:" and the token
                else {
                    System.out.println("Not found Double value :"
                                       + scanner.next());
                }
            }
            scanner.close();
        }
        catch (Exception e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

输出:

Not found Double value :Gfg
Exception thrown: java.util.NoSuchElementException

程序4： 演示IllegalStateException

// Java program to illustrate the
// nextDouble() method of Scanner class in Java
// IllegalStateException
  
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
  
        try {
  
            String s = "Gfg 9 + 6 = 12.0";
  
            // create a new scanner
            // with the specified String Object
            Scanner scanner = new Scanner(s);
  
            // close the scanner
            scanner.close();
            System.out.println("Scanner Closed");
  
            System.out.println("Trying to get "
                               + "next Double value");
  
            while (scanner.hasNext()) {
  
                // if the next is a Double,
                // print found and the Double
                if (scanner.hasNextDouble()) {
                    System.out.println("Found Double value :"
                                       + scanner.nextDouble());
                }
  
                // if no Double is found,
                // print "Not Found:" and the token
                else {
                    System.out.println("Not found Double value :"
                                       + scanner.next());
                }
            }
        }
        catch (Exception e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

输出:

Scanner Closed
Trying to get next Double value
Exception thrown: java.lang.IllegalStateException: Scanner closed

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