Java Scanner hasNextLong()方法及示例

java.util.Scanner 类的 hasNextLong() 方法，如果该扫描器的输入中的下一个标记可以被认为是一个给定弧度的Long值，则返回true。扫描器不会超过任何输入。如果没有将radix作为参数传入，该函数将radix解释为默认radix，并发挥相应的作用。

语法

public boolean hasNextLong(int radix)
            or
public boolean hasNextLong()

参数： 该函数接受一个单一的参数radix，这不是一个强制性参数。它指定了用于将令牌解释为Long值的radix。
返回值： 如果且仅当该扫描器的下一个令牌是默认radix中的有效Long值时，该函数返回true。
异常 ：如果该扫描器被关闭，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
// hasNextLong() method of Scanner class in Java
// with 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 Longs in a string
        scanner.useLocale(Locale.US);
 
        // iterate till end
        while (scanner.hasNext()) {
 
            // check if the scanner's
            // next token is a Long with a radix 3
            System.out.print("" + scanner.hasNextLong(3));
 
            // 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

// Java program to illustrate the
// hasNextLong() 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 Longs in a string
        scanner.useLocale(Locale.US);
 
        // iterate till end
        while (scanner.hasNext()) {
 
            // check if the scanner's
            // next token is a Long with the default radix
            System.out.print("" + scanner.hasNextLong());
 
            // 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3： 演示IllegalStateException的程序

// Java program to illustrate the
// hasNextLong() 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 Longs in a string
            scanner.useLocale(Locale.US);
 
            scanner.close();
 
            // iterate till end
            while (scanner.hasNext()) {
 
                // check if the scanner's
                // next token is a Long with the default radix
                System.out.print("" + scanner.hasNextLong());
 
                // 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#hasNextLong()