private void lengthChanged() {
			long length = 0;
			Long val = lengthField.getValue();
			if (val == null) {
				setOkEnabled(false);
			}
			else {
				length = val.longValue();
			}
			model.setLength(length);
		}
Listener on the length text fields; update other fields
according to the entered value.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/memory/ExpandBlockDialog.java