private void addressChanged() {
			if (dialogType == EXPAND_UP) {
				Address startAddr = startAddressInput.getAddress();
				if (startAddr == null) {
					if (startAddressInput.hasInput()) {
						setStatusText("Invalid Address");
					}
					setOkEnabled(false);
				}
				model.setStartAddress(startAddr);
			}
			else {
				Address endAddr = endAddressInput.getAddress();
				if (endAddr == null) {
					if (endAddressInput.hasInput()) {
						setStatusText("Invalid Address");
					}
					setOkEnabled(false);
				}
				model.setEndAddress(endAddr);
			}
		}
Listener on the AddressInput field; update length field when the 
address input field changes.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/memory/ExpandBlockDialog.java