CODEWITHSUNDEEP
java
dan
dan

Reputation: 127

How to make it so String can't be numeric

If you make a variable type String you can still input numbers.

Example:

"Enter name: 123"

The name is still accepted. How would I make it so a variable name only accepts letters, otherwise an error message will appear?

Upvotes: 2

Views: 554

Answers (5)

user6406577
user6406577

Reputation:

You could check to see whether the string is numeric using a lambda expression:

String myString = "abcdef1234567890";

if (myString.chars().allMatch( Character::isDigit ))

Will output True if the string only contains numbers

Upvotes: 0

JDrost1818
JDrost1818

Reputation: 1126

If using a JTextField or something that allows listeners instead of just the command line, you can prevent the user from inputting numbers with a KeyListener:

userEntry.addKeyListener(new KeyAdapter() {
    @Override
    public void keyTyped(KeyEvent e) {
        if (Character.isDigit(e.getKeyChar())) {
            e.consume();
        }
    }
});

Upvotes: 0

Nico
Nico

Reputation: 319

I don't know any native function to do this, buy you can simply read the string (char per char) and ask if the value is between 65 and 90 (capital letters) or 97 and 122 (normal letters).

The code would be:

    String string = "ABCD";
    boolean hasOtherCharacters = false;
    for ( int i = 0; i < string.length();i++ )
    {
        if ( !(string.charAt(i) >= 65 && string.charAt(i) <= 90) && !(string.charAt(i) >= 97 && string.charAt(i) <= 122) )
        {
            hasOtherCharacters = true;
            break; 
        }
    }

    if ( hasOtherCharacters )
    {
        //WHATEVER YOU WANT

WARNING: This solution applies if your character set is between those ASCCI range.

Upvotes: 1

zeisi
zeisi

Reputation: 5540

Without the help of any additional library you just use Javas pattern matcher:

Pattern p = Pattern.compile("\\D*");

String test1 = "abc";
String test2 = "abc123";

Matcher m1 = p.matcher(test1);
System.out.println("does test1 only contain letters? " + m1.matches());         
//prints true

Matcher m2 = p.matcher(test2);
System.out.println("does test2 only contain letters? " + m2.matches());
//prints false

Upvotes: 1

ConMan
ConMan

Reputation: 1652

You cant necessarily limit the user input to just numbers, however you can validate that input to ensure that it meets your expectations. For example, if you want to ensure that your string does not contain any numbers you can do:

if(str.matches(".*\\d.*")){
   // contains a number
} else{
   // does not contain a number
}

Upvotes: 5

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