How to check if a string is a valid integer? [duplicate]

Question

I have:

 op1 = Integer.parseInt(jTextField1.getText());
 op2 = Integer.parseInt(jTextField2.getText());

However, I want to check first whether the text fields' values can be assigned to integer variables. How do I do that?

I've been going through this for a long time, so, if this was already asked here, forgive me

That's why I said it's hard to explain. I want to check if I can assign a value to a variable — Dannyl
– Dannyl, Commented Feb 15, 2014 at 21:33
Wait, are you saying that if((int i = 0) == true) is valid C code?! — NPE
– NPE, Commented Feb 15, 2014 at 21:34
If it's not a valid integer you'll get an exception. If you don't get the exception, you can assign it. — Dave Newton
– Dave Newton, Commented Feb 15, 2014 at 21:34
Hi @user3314478, and welcome to Stack Overflow. I have edited your question according to your comment on one of the answers. If my edit changed the intent of your question, please feel free to edit further, or go into the revision history and roll back the edit. Do however note that as it stands, this question is very likely to be closed as a duplicate of some other question on the site. — user
– user, Commented Feb 15, 2014 at 21:41

Warlord · Accepted Answer · 2015-03-19 09:44:25Z

16

You can't do if (int i = 0), because assignment returns the assigned value (in this case 0) and if expects an expression that evaluates either to true, or false.

On the other hand, if your goal is to check, whether jTextField.getText() returns a numeric value, that can be parsed to int, you can attempt to do the parsing and if the value is not suitable, NumberFormatException will be raised, to let you know.

try {
    op1 = Integer.parseInt(jTextField1.getText());
} catch (NumberFormatException e) {
    System.out.println("Wrong number");
    op1 = 0;
}

edited Mar 19, 2015 at 9:44

answered Feb 15, 2014 at 21:39

Warlord

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2 Comments

Witiko Over a year ago

The use of an exception as a branching mechanism is discouraged. If the input is likely to be malformed, an explicit validity check should be performed rather than exception catching.

Gerrit Brouwer Over a year ago

Typo: NumericFormatException should be NumberFormatException.

Niroshan Abeywickrama · Accepted Answer · 2014-12-19 09:10:24Z

2

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;
    }

answered Dec 19, 2014 at 9:10

Niroshan Abeywickrama

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Comments

xp500 · Accepted Answer · 2014-02-15 21:55:59Z

1

parseInt throws NumberFormatException if it cannot convert the String to an int. So you should surround the parseInt calls with a try catch block and catch that exception.

answered Feb 15, 2014 at 21:55

xp500

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Comments

Smutje · Accepted Answer · 2014-02-15 21:36:35Z

0

Basically, you have to decide to check if a given string is a valid integer or you simply assume a given string is a valid integer and an exception can occur at parsing.

answered Feb 15, 2014 at 21:36

Smutje

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4 Comments

Dannyl Over a year ago

I want to check if the string is a valid integer

Smutje Over a year ago

Then please search SO for yourself, this topic is as old as Java.

Dannyl Over a year ago

You could have aswered the question instead of complaining .-.

Smutje Over a year ago

Part of asking a question in a forum is thinking about the abstract problem behind the question - and if you're not able to type in "java check string integer" in the search box, sorry.

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