Whitespaces in java

问题:

What are kinds of whitespaces in Java? I need to check in my code if the text contains any whitespaces.

My code is:

if (text.contains(" ") || text.contains("\t") || text.contains("\r") 
       || text.contains("\n"))   
{  
   //code goes here
}   

I already know about \n ,\t ,\r and space.

回答1:

boolean containsWhitespace = false;
for (int i = 0; i < text.length() && !containsWhitespace; i++) {
    if (Character.isWhitespace(text.charAt(i)) {
        containsWhitespace = true;
    }
}
return containsWhitespace;

or, using Guava,

boolean containsWhitespace = CharMatcher.WHITESPACE.matchesAnyOf(text);

回答2:

For a non-regular expression approach, you can check Character.isWhitespace for each character.

boolean containsWhitespace(String s) {
    for (int i = 0; i < s.length(); ++i) {
        if (Character.isWhitespace(s.charAt(i)) {
            return true;
        }
    }
    return false;
}

---

Which are the white spaces in Java?

The documentation specifies what Java considers to be whitespace:

public static boolean isWhitespace(char ch)

Determines if the specified character is white space according to Java. A character is a Java whitespace character if and only if it satisfies one of the following criteria:

• It is a Unicode space character (SPACE_SEPARATOR, LINE_SEPARATOR, or PARAGRAPH_SEPARATOR) but is not also a non-breaking space ('\u00A0', '\u2007', '\u202F').
• It is '\u0009', HORIZONTAL TABULATION.
• It is '\u000A', LINE FEED.
• It is '\u000B', VERTICAL TABULATION.
• It is '\u000C', FORM FEED.
• It is '\u000D', CARRIAGE RETURN.
• It is '\u001C', FILE SEPARATOR.
• It is '\u001D', GROUP SEPARATOR.
• It is '\u001E', RECORD SEPARATOR.
• It is '\u001F', UNIT SEPARATOR.

回答3:

Use Character.isWhitespace() rather than creating your own.

In Java how does one turn a String into a char or a char into a String?

回答4:

If you can use apache.commons.lang in your project, the easiest way would be just to use the method provided there:

public static boolean containsWhitespace(CharSequence seq)

Check whether the given CharSequence contains any whitespace characters.

Parameters:

seq - the CharSequence to check (may be null) 

Returns:

true if the CharSequence is not empty and contains at least 1 whitespace character

It handles empty and null parameters and provides the functionality at a central place.

回答5:

From sun docs:

\s A whitespace character: [ \t\n\x0B\f\r]

The simplest way is to use it with regex.

回答6:

If you want to consider a regular expression based way of doing it

if(text.split("\\s").length > 1){
    //text contains whitespace
}

回答7:

boolean whitespaceSearchRegExp(String input) {

    return java.util.regex.Pattern.compile("\\s").matcher(input).find();

} 

回答8:

Why don't you check if text.trim() has a different length? :

if(text.length() == text.trim().length() || otherConditions){
    //your code
}