Java Scanner nextBoolean()方法及示例

java.util.Scanner 类的 nextBoolean() 方法将输入的下一个标记扫描为布尔值。如果翻译成功，扫描器就会向前推进，越过匹配的输入。

语法

public boolean nextBoolean()

参数： 该函数不接受任何参数。

返回值： 该函数返回从输入中 扫描出来的布尔值 。

异常： 该函数抛出三种异常，如下所述。

• InputMismatchException： 如果下一个标记不是一个有效的布尔值
• 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
// nextBoolean() 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 true 9 + 6 = 12.0 false";
  
        // create a new scanner
        // with the specified String Object
        Scanner scanner = new Scanner(s);
  
        while (scanner.hasNext()) {
  
            // if the next is a Boolean,
            // print found and the Boolean
            if (scanner.hasNextBoolean()) {
                System.out.println("Found Boolean value :"
                                   + scanner.nextBoolean());
            }
  
            // if no Boolean is foucnd,
            // print "Not Found:" and the token
            else {
                System.out.println("Not found Boolean() value :"
                                   + scanner.next());
            }
        }
        scanner.close();
    }
}

输出:

Not found Boolean() value :Gfg
Found Boolean value :true
Not found Boolean() value :9
Not found Boolean() value :+
Not found Boolean() value :6
Not found Boolean() value :=
Not found Boolean() value :12.0
Found Boolean value :false

程序2： 演示InputMismatchException

// Java program to illustrate the
// nextBoolean() 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 Boolean
                // print found and the Boolean
                // since the value 60 is out of range
                // it throws an exception
  
                System.out.println("Next Boolean value :"
                                   + scanner.nextBoolean());
            }
            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
// nextBoolean() 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 Boolean value
            // more times than the scanner
            // Hence it will throw exception
            for (int i = 0; i < 5; i++) {
  
                // if the next is a Boolean,
                // print found and the Boolean
                if (scanner.hasNextBoolean()) {
                    System.out.println("Found Boolean value :"
                                       + scanner.nextBoolean());
                }
  
                // if no Boolean is found,
                // print "Not Found:" and the token
                else {
                    System.out.println("Not found Boolean value :"
                                       + scanner.next());
                }
            }
            scanner.close();
        }
        catch (Exception e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

输出:

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

程序4： 演示IllegalStateException

// Java program to illustrate the
// nextBoolean() 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 Boolean value");
  
            while (scanner.hasNext()) {
  
                // if the next is a Boolean,
                // print found and the Boolean
                if (scanner.hasNextBoolean()) {
                    System.out.println("Found Boolean value :"
                                       + scanner.nextBoolean());
                }
  
                // if no Boolean is found,
                // print "Not Found:" and the token
                else {
                    System.out.println("Not found Boolean value :"
                                       + scanner.next());
                }
            }
        }
        catch (Exception e) {
            System.out.println("Exception thrown: " + e);
        }
    }
}

输出:

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

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