程序设计语言概念(ConceptsofProgrammingLanguages)英文第10版第14章.ppt

* * * * * * * * * * * * * * * * * * * * Copyright ? 2012 Addison-Wesley. All rights reserved. 1-* The finally Clause Can appear at the end of a try construct Form: finally { ... } Purpose: To specify code that is to be executed, regardless of what happens in the try construct Copyright ? 2012 Addison-Wesley. All rights reserved. 1-* Example A try construct with a finally clause can be used outside exception handling try { for (index = 0; index 100; index++) { … if (…) { return; } //** end of if } //** end of try clause finally { … } //** end of try construct Copyright ? 2012 Addison-Wesley. All rights reserved. 1-* Assertions Statements in the program declaring a boolean expression regarding the current state of the computation When evaluated to true nothing happens When evaluated to false an AssertionError exception is thrown Can be disabled during runtime without program modification or recompilation Two forms assert condition; assert condition: expression; Copyright ? 2012 Addison-Wesley. All rights reserved. 1-* Evaluation The types of exceptions makes more sense than in the case of C++ The throws clause is better than that of C++ (The throw clause in C++ says little to the programmer) The finally clause is often useful The Java interpreter throws a variety of exceptions that can be handled by user programs Copyright ? 2012 Addison-Wesley. All rights reserved. 1-* Introduction to Event Handling An event is a notification that something specific has occurred, such as a mouse click on a graphical button The event handler is a segment of code that is executed in response to an event Copyright ? 2012 Addison-Wesley. All rights reserved. 1-* Java Swing GUI Components Text box is an object of class JTextField Radio button is an object of class JRadioButton Applet’s display is a frame, a multilayered structure Content pane is one layer, where applets put output GUI components can be placed in a frame Layout manager objects are used to control