--- Klass.java ---------------------------------------------

public class Klass implements Iface {
	public String getInputText(boolean doit) throws InputNotProvidedException {
		if (doit)
			throw new InputNotProvidedException();
		
		return "was auch immer";
	}
	
	public static void main(String[] args) {
		Klass klass = new Klass();
		
		try {
			klass.getInputText(false);
			klass.getInputText(true);
		}
		catch (InputNotProvidedException ex) {
		}
	}
}

--- Iface.java ---------------------------------------------------

public interface Iface {
	public String getInputText(boolean doit) throws InputNotProvidedException;
}

--- InputNotProvidedException.java -------------------------------------

public class InputNotProvidedException extends Exception {
	private static final long serialVersionUID = 1L;
}