Java中的 Scanner nextDouble() 方法和示例

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，扫描仪会超过匹配的输入。

句法：

public double nextDouble()

参数：该函数不接受任何参数。

返回值：此函数返回从输入扫描的 Double 。

异常：该函数抛出三个异常，如下所述：

• InputMismatchException：如果下一个标记与 Double 正则表达式不匹配，或者超出范围
• NoSuchElementException：如果输入用尽则抛出
• IllegalStateException：如果此扫描仪关闭则抛出

下面的程序说明了上述函数：

方案一：

// 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： https: Java/util/Scanner.html#nextDouble()