How do I catch a NoSuchElementException?

问题:

I am making a function that returns a Boolean type of whether a String has enough tokens. I do this by using this code:

public boolean isEnoughTokens(int tokens, String problem) {
        try {
            StringTokenizer token = new StringTokenizer(problem);
            return true;
        } catch (NoSuchElementException ) {

        }
    }

The problem is that I haven't figured out how to catch a No such element exception. I think it's super simple but still didn't figure out how to do it.

Thanks, any help will be appreciated!!!

回答1:

Here's how I might do it. Not what you had in mind, but I wanted to show you JUnit.

StringUtils.java:

package utils;

import java.util.Arrays;
import java.util.List;

/**
 * @author Michael
 * @link https://stackoverflow.com/questions/41006856/how-do-i-catch-a-nosuchelementexception?noredirect=1#comment69222264_41006856
 */
public class StringUtils {

    private StringUtils() {}

    public static List<String> tokenize(String str) {
        String [] tokens = new String[0];
        if (isNotBlankOrNull(str)) {
            str = str.trim();
            tokens = str.split("\\s+");
        }
        return Arrays.asList(tokens);
    }

    public static boolean isBlankOrNull(String s) {
        return ((s == null) || (s.trim().length() == 0));
    }

    public static boolean isNotBlankOrNull(String s) {
        return !isBlankOrNull(s);
    }

    public static boolean hasSufficientTokens(int numTokens, String str) {
        return (numTokens >= 0) && tokenize(str).size() >= numTokens;
    }
}

StringUtilsTest.java:

package utils;

import org.junit.Assert;
import org.junit.Test;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
 * Created by Michael
 * Creation date 12/6/2016.
 * @link https://stackoverflow.com/questions/41006856/how-do-i-catch-a-nosuchelementexception?noredirect=1#comment69222264_41006856
 */
public class StringUtilsTest {

    @Test
    public void testIsNotBlankOrNull_NullString() {
        Assert.assertFalse(StringUtils.isNotBlankOrNull(null));
    }

    @Test
    public void testIsNotBlankOrNull_EmptyString() {
        Assert.assertFalse(StringUtils.isNotBlankOrNull(""));
    }

    @Test
    public void testIsNotBlankOrNull_BlankString() {
        Assert.assertFalse(StringUtils.isNotBlankOrNull("        "));
    }

    @Test
    public void testIsNotBlankOrNull_FullString() {
        Assert.assertTrue(StringUtils.isNotBlankOrNull("I'm not null, blank, or empty"));
    }

    @Test
    public void testTokenize_NullString() {
        // setup
        List<String> expected = Collections.EMPTY_LIST;
        // exercise
        List<String> actual = StringUtils.tokenize(null);
        // assert
        Assert.assertEquals(expected, actual);
    }

    @Test
    public void testTokenize_EmptyString() {
        // setup
        List<String> expected = Collections.EMPTY_LIST;
        // exercise
        List<String> actual = StringUtils.tokenize("");
        // assert
        Assert.assertEquals(expected, actual);
    }

    @Test
    public void testTokenize_BlankString() {
        // setup
        List<String> expected = Collections.EMPTY_LIST;
        // exercise
        List<String> actual = StringUtils.tokenize("        ");
        // assert
        Assert.assertEquals(expected, actual);
    }

    @Test
    public void testTokenize_FullString() {
        // setup
        List<String> expected = Arrays.asList("I'm", "not", "null,", "blank,", "or", "empty");
        // exercise
        List<String> actual = StringUtils.tokenize("    I'm not     null,    blank, or empty    ");
        // assert
        Assert.assertEquals(expected.size(), actual.size());
        Assert.assertEquals(expected, actual);
    }

    @Test
    public void hasSufficientTokens_NegativeTokens() {
        // setup
        int numTokens = -1;
        String str = "    I'm not     null,    blank, or empty    ";
        // exercise
        // assert
        Assert.assertFalse(StringUtils.hasSufficientTokens(numTokens, str));
    }

    @Test
    public void hasSufficientTokens_InsufficientTokens() {
        // setup
        String str = "    I'm not     null,    blank, or empty    ";
        int numTokens = StringUtils.tokenize(str).size() + 1;
        // exercise
        // assert
        Assert.assertFalse(StringUtils.hasSufficientTokens(numTokens, str));
    }

    @Test
    public void hasSufficientTokens_NullString() {
        // setup
        String str = "";
        int numTokens = StringUtils.tokenize(str).size();
        // exercise
        // assert
        Assert.assertTrue(StringUtils.hasSufficientTokens(numTokens, str));
    }

    @Test
    public void hasSufficientTokens_Success() {
        // setup
        String str = "    I'm not     null,    blank, or empty    ";
        int numTokens = StringUtils.tokenize(str).size();
        // exercise
        // assert
        Assert.assertTrue(StringUtils.hasSufficientTokens(numTokens, str));
    }
}

It's not a good idea to use exceptions for program logic.

StringTokenizer is a JDK 1.0 vintage class. It's stood the test of time, but I would not recommend going all the way back to 1995.

回答2:

I think I found the answer to my own question! I was messing around and thanks to you informing me about the countTokens() function I came up with this!

public boolean isEnoughTokens(int tokens, String problem) {
        try {
            StringTokenizer token = new StringTokenizer(problem);
            if (token.countTokens() == tokens) {
                return true;
            }
            else {
                return false;
            }
        } catch (NoSuchElementException e) {
            return false;
        }
    }

I don't know if there is any error but so far when I tested it, it works!