java check if string is 4 digit number code example

Example 1: java check if string is number

try {
    int n = Integer.parseInt(str);
} catch (NumberFormatException e) {
    // str is not a number
}

Example 2: how to check if a string has only numbers in java

// Java program for the above approach
// contains only digits
class GFG {

	// Function to check if a string
	// contains only digits
	public static boolean
	onlyDigits(String str, int n)
	{
		// Traverse the string from
		// start to end
		for (int i = 0; i < n; i++) {

			// Check if character is
			// digit from 0-9
			// then return true
			// else false
			if (str.charAt(i) >= '0'
				&& str.charAt(i) <= '9') {
				return true;
			}
			else {
				return false;
			}
		}
		return false;
	}

	// Driver Code
	public static void main(String args[])
	{
		// Given string str
		String str = "1234";
		int len = str.length();

		// Function Call
		System.out.println(onlyDigits(str, len));
	}
}