What's the best way to check if a String represents an integer in Java?

Question

I normally use the following idiom to check if a String can be converted to an integer.

public boolean isInteger( String input ) {
    try {
        Integer.         


        

Answer 1

There is guava version:

import com.google.common.primitives.Ints;

Integer intValue = Ints.tryParse(stringValue);

It will return null instead of throwing an exception if it fails to parse string.

Answer 2

org.apache.commons.lang.StringUtils.isNumeric 

though Java's standard lib really misses such utility functions

I think that Apache Commons is a "must have" for every Java programmer

too bad it isn't ported to Java5 yet

Answer 3

It partly depend on what you mean by "can be converted to an integer".

If you mean "can be converted into an int in Java" then the answer from Jonas is a good start, but doesn't quite finish the job. It would pass 999999999999999999999999999999 for example. I would add the normal try/catch call from your own question at the end of the method.

The character-by-character checks will efficiently reject "not an integer at all" cases, leaving "it's an integer but Java can't handle it" cases to be caught by the slower exception route. You could do this bit by hand too, but it would be a lot more complicated.

Answer 4

What you did works, but you probably shouldn't always check that way. Throwing exceptions should be reserved for "exceptional" situations (maybe that fits in your case, though), and are very costly in terms of performance.

Answer 5

This would work only for positive integers.

public static boolean isInt(String str) {
    if (str != null && str.length() != 0) {
        for (int i = 0; i < str.length(); i++) {
            if (!Character.isDigit(str.charAt(i))) return false;
        }
    }
    return true;        
}

Answer 6

This works for me. Simply to identify whether a String is a primitive or a number.

private boolean isPrimitive(String value){
        boolean status=true;
        if(value.length()<1)
            return false;
        for(int i = 0;i<value.length();i++){
            char c=value.charAt(i);
            if(Character.isDigit(c) || c=='.'){

            }else{
                status=false;
                break;
            }
        }
        return status;
    }