Remove white space from string without using trim method?

Question

given string is \'_home sweet home__\' if user enter the mode as 0 then o/p should be \'home sweet home__\' if user enter the mod

Answer 1

You could try something like this:

/**
 * Remove white spaces from string according to mode
 * 
 * @param str string
 * @param mode mode 0=leading, 1=trailing, 2=leading+trailing
 * @param result - result buffer
 * @return number of white spaces removed
 */
public int removeWhiteSpacesByMode(String str, int mode, StringBuilder result) {
    int n = 0;
    switch(mode) {
        case 0:
            n = removeLeadingWhiteSpaces(str, result);
            break;
        case 1:
            n = removeTrailingWhiteSpaces(str, result);
            break;
        case 2:
            StringBuilder tmp = new StringBuilder();
            n = removeTrailingWhiteSpaces(str, tmp);
            n += removeLeadingWhiteSpaces(tmp.toString(), result);
            break;
        default:
            throw new IllegalArgumentException("mode=" + mode);
    }
    return n;
}

private int removeTrailingWhiteSpaces(String str, StringBuilder result) {
    int n = 0;
    if(str != null && result != null) {
        n = str.length()-1;
        while(Character.isWhitespace(str.charAt(n))) {
            n--;
        }
        n++;
        for(int j = 0; j < n; j++) {
            result.append(str.charAt(j));
        }
        n = str.length() - n;
    }
    return n;
}

private int removeLeadingWhiteSpaces(String str, StringBuilder result) {
    int n = 0;
    if(str != null && result != null) {
        while(Character.isWhitespace(str.charAt(n))) {
            n++;
        }
        for(int j = n; j < str.length(); j++) {
            result.append(str.charAt(j));
        }
    }
    return n;
}

It makes use a of the method Character#isWhitespace to check whether a character is white space or not and a StringBuilder to build the result. The return value is the number of white paces removed.

If you want to have a method to just count the white spaces in a string you can loop over the entire string, check each character using Character#isWhitespace and increment a variable if it return true.

Finally here is some testing:

@Test
public void removeWhiteSpacesByMode() {
    String str = " home sweet home  ";
    StringBuilder result = null;
    int numberOfWhiteSpacesRemoved = 0;

    numberOfWhiteSpacesRemoved = removeWhiteSpacesByMode(str, 0, null);
    Assert.assertEquals(numberOfWhiteSpacesRemoved, 0);

    result = new StringBuilder();
    numberOfWhiteSpacesRemoved = removeWhiteSpacesByMode(null, 0, result);
    Assert.assertEquals(0, result.length());
    Assert.assertEquals(numberOfWhiteSpacesRemoved, 0);

    try {
        result = new StringBuilder();
        numberOfWhiteSpacesRemoved = 0;
        numberOfWhiteSpacesRemoved = removeWhiteSpacesByMode(null, 4, result);
        Assert.fail("mode 4 should not have been accepted");
    } catch(IllegalArgumentException e) {
        Assert.assertEquals("mode=4", e.getMessage());
        Assert.assertEquals(0, result.length());
        Assert.assertEquals(numberOfWhiteSpacesRemoved, 0);
    }

    result = new StringBuilder();
    numberOfWhiteSpacesRemoved = removeWhiteSpacesByMode(str, 0, result);
    Assert.assertEquals("home sweet home  ", result.toString());
    Assert.assertEquals(numberOfWhiteSpacesRemoved, 1);

    result = new StringBuilder();
    numberOfWhiteSpacesRemoved = removeWhiteSpacesByMode(str, 1, result);
    Assert.assertEquals(" home sweet home", result.toString());
    Assert.assertEquals(numberOfWhiteSpacesRemoved, 2);

    result = new StringBuilder();
    numberOfWhiteSpacesRemoved = removeWhiteSpacesByMode(str, 2, result);
    Assert.assertEquals("home sweet home", result.toString());
    Assert.assertEquals(numberOfWhiteSpacesRemoved, 3);
}