CleanCode::Code::Branches (IF2)

We've covered switch statements and static lookup tables in IF1. For completeness, we'll mention dynamic lookup tables, but the treatment here is fairly elementary. Dynamic method lookup is a powerful capability in Java, but it does incur some overhead. What it provides, however, is the ability to invoke a method just by its string name. One could, then, ask a user to type in a method name, and then the program could execute that method. The example below provides one example of a basic skeleton to invoke a method dynamically. This code snippet requires that you set up action commands on events which trigger the ActionListener containing this actionPerformed handler. The event message is then passed to the method after the method is looked up by name.

EXAMPLEJava

Instead of:

private final String CMD_REFRESH = "doRefresh";
private final String CMD_CLEAR_HISTORY = "doClear";
private final String CMD_COPY_TAB= "doCopyTab";
private final String CMD_PASTE_COOKIE = "doPasteCookie";
private final String CMD_SAVE_HISTORY = "doSaveHistory";
. . .

public void actionPerformed(ActionEvent event) {
	String cmd = event.getActionCommand();
	if      (cmd.equals(CMD_REFRESH))       { doRefresh(event); }
	else if (cmd.equals(CMD_CLEAR_HISTORY)) { doClear(event); }
	else if (cmd.equals(CMD_COPY_TAB))      { doCopyTab(event); }
	else if (cmd.equals(CMD_PASTE_COOKIE))  { doPasteCookie(event); }
	else if (cmd.equals(CMD_SAVE_HISTORY))  { doSaveHistory(event); }
	. . .
}

Use:

public void actionPerformed(ActionEvent event) {
	String cmd = event.getActionCommand();
	try {
		Method m = this.getClass().getMethod(
			cmd, new Class[] { ActionEvent.class });
		m.invoke(this, new Object[] { event });
	}
	catch (Exception exc) { ... }
}