Basic integer and double parser with error messages

Parse.java

package com.aidensheeran.prg10EmployeeClass;

import com.aidensheeran.prg10EmployeeClass.GUI.Sign;

@SuppressWarnings("null")
public class Parse {

	public static boolean isDouble(String string) {
		string = string.trim();
		try {
			Double.parseDouble(string);
		} catch(NumberFormatException error) {
			return false;
		}
		return true;
	}
	public static boolean isInt(String string) {
		string = string.trim();
		if (string.contains(".")) { GUI.out("Input must be an integer!", Sign.CAUTION); return false; }
		try {
			Integer.parseInt(string);
		} catch(NumberFormatException error) {
			return false;
		}
		return true;
	}
	
	public static double doubles(String string) {
		double out = 0;
		string = string.trim();
		try {
			out = Double.parseDouble(string);
		} catch(NumberFormatException error) {
			GUI.out("ERROR: " + error.getMessage(), Sign.CAUTION);
			return (Double) null;
		}
		return out;
	}
	public static int ints(String string) {
		int out = 0;
		string = string.trim();
		if (string.contains(".")) { GUI.out("Input must be an integer!", Sign.CAUTION); return out; }
		try {
			out = Integer.parseInt(string);
		} catch(NumberFormatException error) {
			GUI.out("ERROR: " + error.getMessage(), Sign.CAUTION);
			return (Integer) null;
		}
		return out;
	}

}