Part IV: Savvy Java Techniques in Java

Make Code 39 in Java Part IV: Savvy Java Techniques

IInterestingly enough, you don t see the words I won t get printed in Figure 12-14 Because the catch clause s execution throws its own uncaught exception, the computer never makes it down past the try-catch-finally statement So, the computer goes back to where it left off in the main method Back in the main method, word of the doSomething method s ArithmeticException mishaps causes execution to jump into a catch clause The computer prints Exception caught in main, and then this terrible nightmare of a run is finished

ou re near the end of the book, and the time has come to sum it all up This part of the book is your slam-bam, two-thousand-words-or-less resource for Java What You didn t read every word in the chapters before this one That s okay You can pick up a lot of useful information in this Part of Tens

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Checking your capitalization and value comparisons Watching out for fall-through Putting methods, listeners, and constructors where they belong Using static and nonstatic references Avoiding other heinous errors

he only people who never make mistakes are the people who never do anything at all One of my college professors said that I don t remember the professor s name, so I can t give him proper credit I guess that s my mistake

Java is a case-sensitive language, so you really have to mind your Ps and Qs along with every other letter of the alphabet Here are some things to keep in mind as you create Java programs: Java s keywords are all completely lowercase For instance, in a Java if statement, the word if can t be If or IF When you use names from the Java API (Application Programming Interface), the case of the names has to match what appears in the API You also need to make sure that the names you make up yourself are capitalized the same way throughout your entire program If you declare a myAccount variable, you can t refer to it as MyAccount, myaccount, or Myaccount If you capitalize the variable name two different ways, Java thinks you re referring to two completely different variables For more info on Java s case-sensitivity, see 3

If you don t break out of a switch statement, you get fall-through For instance, if the value of verse is 3, the following code prints all three lines Last refrain, He s a pain, and Has no brain switch (verse) { case 3: outprint( Last refrain, ); outprintln( last refrain, ); case 2: outprint( He s a pain, ); outprintln( he s a pain, ); case 1: outprint( Has no brain, ); outprintln( has no brain, ); } For the full story, see 5

When you compare two values with one another, you use a double equal sign The line if (inputNumber == randomNumber) is correct, but the line if (inputNumber = randomNumber) is not correct For a full report, see 5

Here s a constructor for a Java frame:

public SimpleFrame() { JButton button = new JButton( Thank you ); setTitle( Katie Feltman and Heidi Unger ); setLayout(new FlowLayout()); add(button); buttonaddActionListener(this); setSize(300, 100); setVisible(true); } Whatever you do, don t forget the call to the add method Without this call, you go to all the work of creating a button, but the button doesn t show up on your frame For an introduction to such issues, see 9

Look again at the previous section s code to construct a SimpleFrame If you forget the call to addActionListener, nothing happens when you click the button Clicking the button harder a second time doesn t help For the rundown on listeners, see 16, which is on the CD-ROM