Java tutorial
/* * Copyright (c) 2000 David Flanagan. All rights reserved. * This code is from the book Java Examples in a Nutshell, 2nd Edition. * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied. * You may study, use, and modify it for any non-commercial purpose. * You may distribute it non-commercially as long as you retain this notice. * For a commercial use license, or to purchase the book (recommended), * visit http://www.davidflanagan.com/javaexamples2. */ import java.awt.event.*; import java.beans.*; import java.lang.reflect.*; import java.io.*; import java.util.*; /** * This class represents a Method, the list of arguments to be passed to that * method, and the object on which the method is to be invoked. The invoke() * method invokes the method. The actionPerformed() method does the same thing, * allowing this class to implement ActionListener and be used to respond to * ActionEvents generated in a GUI or elsewhere. The static parse() method * parses a string representation of a method and its arguments. */ public class Command implements ActionListener { Method m; // The method to be invoked Object target; // The object to invoke it on Object[] args; // The arguments to pass to the method // An empty array; used for methods with no arguments at all. static final Object[] nullargs = new Object[] {}; /** This constructor creates a Command object for a no-arg method */ public Command(Object target, Method m) { this(target, m, nullargs); } /** * This constructor creates a Command object for a method that takes the * specified array of arguments. Note that the parse() method provides * another way to create a Command object */ public Command(Object target, Method m, Object[] args) { this.target = target; this.m = m; this.args = args; } /** * Invoke the Command by calling the method on its target, and passing the * arguments. See also actionPerformed() which does not throw the checked * exceptions that this method does. */ public void invoke() throws IllegalAccessException, InvocationTargetException { m.invoke(target, args); // Use reflection to invoke the method } /** * This method implements the ActionListener interface. It is like invoke() * except that it catches the exceptions thrown by that method and rethrows * them as an unchecked RuntimeException */ public void actionPerformed(ActionEvent e) { try { invoke(); // Call the invoke method } catch (InvocationTargetException ex) { // but handle the exceptions throw new RuntimeException("Command: " + ex.getTargetException().toString()); } catch (IllegalAccessException ex) { throw new RuntimeException("Command: " + ex.toString()); } } /** * This static method creates a Command using the specified target object, * and the specified string. The string should contain method name followed * by an optional parenthesized comma-separated argument list and a * semicolon. The arguments may be boolean, integer or double literals, or * double-quoted strings. The parser is lenient about missing commas, * semicolons and quotes, but throws an IOException if it cannot parse the * string. */ public static Command parse(Object target, String text) throws IOException { String methodname; // The name of the method ArrayList args = new ArrayList(); // Hold arguments as we parse them. ArrayList types = new ArrayList(); // Hold argument types. // Convert the string into a character stream, and use the // StreamTokenizer class to convert it into a stream of tokens StreamTokenizer t = new StreamTokenizer(new StringReader(text)); // The first token must be the method name int c = t.nextToken(); // read a token if (c != t.TT_WORD) // check the token type throw new IOException("Missing method name for command"); methodname = t.sval; // Remember the method name // Now we either need a semicolon or a open paren c = t.nextToken(); if (c == '(') { // If we see an open paren, then parse an arg list for (;;) { // Loop 'till end of arglist c = t.nextToken(); // Read next token if (c == ')') { // See if we're done parsing arguments. c = t.nextToken(); // If so, parse an optional semicolon if (c != ';') t.pushBack(); break; // Now stop the loop. } // Otherwise, the token is an argument; figure out its type if (c == t.TT_WORD) { // If the token is an identifier, parse boolean literals, // and treat any other tokens as unquoted string literals. if (t.sval.equals("true")) { // Boolean literal args.add(Boolean.TRUE); types.add(boolean.class); } else if (t.sval.equals("false")) { // Boolean literal args.add(Boolean.FALSE); types.add(boolean.class); } else { // Assume its a string args.add(t.sval); types.add(String.class); } } else if (c == '"') { // If the token is a quoted string args.add(t.sval); types.add(String.class); } else if (c == t.TT_NUMBER) { // If the token is a number int i = (int) t.nval; if (i == t.nval) { // Check if its an integer // Note: this code treats a token like "2.0" as an int! args.add(new Integer(i)); types.add(int.class); } else { // Otherwise, its a double args.add(new Double(t.nval)); types.add(double.class); } } else { // Any other token is an error throw new IOException( "Unexpected token " + t.sval + " in argument list of " + methodname + "()."); } // Next should be a comma, but we don't complain if its not c = t.nextToken(); if (c != ',') t.pushBack(); } } else if (c != ';') { // if a method name is not followed by a paren t.pushBack(); // then allow a semi-colon but don't require it. } // We've parsed the argument list. // Next, convert the lists of argument values and types to arrays Object[] argValues = args.toArray(); Class[] argtypes = (Class[]) types.toArray(new Class[argValues.length]); // At this point, we've got a method name, and arrays of argument // values and types. Use reflection on the class of the target object // to find a method with the given name and argument types. Throw // an exception if we can't find the named method. Method method; try { method = target.getClass().getMethod(methodname, argtypes); } catch (Exception e) { throw new IOException("No such method found, or wrong argument " + "types: " + methodname); } // Finally, create and return a Command object, using the target object // passed to this method, the Method object we obtained above, and // the array of argument values we parsed from the string. return new Command(target, method, argValues); } public static void main(String[] args) throws IOException { javax.swing.JFrame f = new javax.swing.JFrame("Command Test"); javax.swing.JButton b1 = new javax.swing.JButton("Tick"); javax.swing.JButton b2 = new javax.swing.JButton("Tock"); javax.swing.JLabel label = new javax.swing.JLabel("Hello world"); java.awt.Container pane = f.getContentPane(); pane.add(b1, java.awt.BorderLayout.WEST); pane.add(b2, java.awt.BorderLayout.EAST); pane.add(label, java.awt.BorderLayout.NORTH); b1.addActionListener(Command.parse(label, "setText(\"tick\");")); b2.addActionListener(Command.parse(label, "setText(\"tock\");")); f.pack(); f.show(); } }