Part II: Writing Your Own Java Programs - Get a Free Blog

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12 Part I: Revving Up More free books @ www.BingEbook.com From Your Mind to the Computer’s Processor When you create a new computer program, you go through a multistep process. The process involves three important tools: Compiler: A compiler translates your code into computer-friendly (human-unfriendly) instructions. Virtual machine: A virtual machine steps through the computer-friendly instructions. Application programming interface: An application programming interface contains useful prewritten code. The next three sections describe each of the three tools. Translating your code You may have heard that computers deal with zeros and ones. That’s certainly true, but what does it mean? Well, for starters, computer circuits don’t deal directly with letters of the alphabet. When you see the word Start on your computer screen, the computer stores the word internally as 01010011 01110100 01100001 01110010 01110100. That feeling you get of seeing a friendly looking five-letter word is your interpretation of the computer screen’s pixels, and nothing more. Computers break everything down into very low-level, unfriendly sequences of zeros and ones, and then put things back together so that humans can deal with the results. So what happens when you write a computer program? Well, the program has to get translated into zeros and ones. The official name for the translation process is compilation. Without compilation, the computer can’t run your program. I compiled the code in Listing 1-1. Then I did some harmless hacking to help me see the resulting zeros and ones. What I saw was the mishmash in Figure 1-1. The compiled mumbo jumbo in Figure 1-1 goes by many different names: Most Java programmers call it bytecode. I often call it a .class file. That’s because, in Java, the bytecode gets stored in files named SomethingOrOther.class. To emphasize the difference, Java programmers call Listing 1-1 the source code, and refer to the zeros and ones in Figure 1-1 as object code.
Figure 1-1: My computer understands these zeros and ones, but I don’t. Figure 1-2: The computer compiles source code to create object code. More free books @ www.BingEbook.com To visualize the relationship between source code and object code, see Figure 1-2. You can write source code, and then get the computer to create object code from your source code. To create object code, the computer uses a special software tool called a compiler. Your computer’s hard drive may have a file named javac or javac.exe. This file contains that special software tool — the compiler. (Hey, how about that? The word javac stands for “Java compiler!”) As a Java programmer, you often tell your computer to build some new object code. Your computer fulfills this wish by going behind the scenes and running the instructions in the javac file. Running code Chapter 1: Getting Started Several years ago, I spent a week in Copenhagen. I hung out with a friend who spoke both Danish and English fluently. As we chatted in the public park, I vaguely noticed some kids orbiting around us. I don’t speak a word of Danish, so I assumed that the kids were talking about ordinary kid stuff. 13
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Page 5 and 6: About the Author More free books @
Page 7 and 8: Dedication More free books @ www.Bi
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Figure 4-6: Calling the System.out.
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In This Chapter Chapter 5 Composing
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Figure 5-1: What part of the word
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1. Launch JCreator. 2. From JCreato
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Figure 5-6: The computer substitute
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Also, the table’s story has a sur
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At first you may think this guy has
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Figure 5-8: A helpful error message
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Chapter 5: Composing a Program The
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Avoid the knee-jerk response. Some
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Chapter 5: Composing a Program One
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Figure 5-13: Whadaya mean “NoSuch
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Spaces and indentation Java isn’t
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Chapter 6 Using the Building Blocks
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Figure 6-2: A variable (before and
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Figure 6-4: Reading an assignment s
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Figure 6-6: An extreme close-up of
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Figure 6-7: Getting the value of a
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Methods and assignments Note how I
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You can’t drag statements outside
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In This Chapter Processing whole n
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eflected nicely in Java. In Listing
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Figure 7-4: How to make six kids ve
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Figure 7-5: Hey, bud! Got change fo
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Figure 7-7: Using preincrement. Mor
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To cram a double value into an int
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Look at the bold line of code in Fi
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Are you trying to decide between us
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Figure 7-13: Storing the digits 422
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Chapter 8 Numbers? Who Needs Number
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Figure 8-2: The action in Listing 8
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More free books @ www.BingEbook.com
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Figure 8-5: Stop those pots! The co
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I wish I could give you twelve simp
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To represent a lone character in th
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Figure 8-11: The Fahrenheit tempera
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Figure 8-13: The Fahrenheit variabl
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In This Chapter Chapter 9 Forks in
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Figure 9-3: An if statement and its
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Figure 9-4: The allknowing Java pro
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Randomness makes me dizzy When you
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Anyway, whether you’re skinning c
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Anyway, notice that the value of ra
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An elegant way to think about if st
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In This Chapter Chapter 10 Which Wa
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Figure 10-2: Admission prices for B
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Figure 10-4: The choices in Listing
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Figure 10-6: Running the code in Li
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Figure 10-8: A capital offense. Fig
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} } More free books @ www.BingEbook
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Listing 10-8: Proud Winners and Sor
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Chapter 11 How to Flick a Virtual S
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Figure 11-2: A fork with eleven pro
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Figure 11-4: How many days until th
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Figure 11-6: From your mind to the
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In This Chapter Chapter 12 Around a
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Figure 12-1: Momma needs a new pair
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Figure 12-4: Look! I rolled a seven
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Figure 12-5: You win sum; you lose
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Figure 12-8: An incorrect run. You
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If you’ve read this whole section
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Figure 12-11: Jumping into a loop.
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Figure 12-13: The strategy in Listi
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In This Chapter Chapter 13 Piles of
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218 Part III: Controlling the Flow
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Figure 15-5: A readable display of
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Figure 15-6: No! Don’t do it! Mor
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Figure 15-7: Here we go loop, do lo
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That’s why my writing a Java prog
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In general, a someEnumTypeName.valu
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Figure 15-10: Entering loops for th
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Figure 15-14: Traveling a second ti
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In This Chapter Using for loops to
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Listing 16-1 uses a for loop — a
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Figure 16-3: A few one-room reports
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Listing 16-3 has a big fat conditio
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guestsIn[6] = 0; On one weekday, bu
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In This Chapter Creating classes C
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Figure 17-2: The code in Listing 17
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The two programs (in Listings 17-1
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Listing 17-4: What It Means to Be a
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Figure 17-6: From one class come th
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Figure 17-7: A table of purchases.
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Chapter 18 Using Methods and Variab
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Putting String variables to good us
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To display a String value, you can
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Figure 18-4: This looks even worse.
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Figure 18-6: Viewing the String cla
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Combining and using data At this po
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Turning strings into numbers The co
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Figure 18-9: Do you have change for
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Packages and import declarations In
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That’s very nice! How about the S
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class Check { int number; double am
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Chapter 19 Creating New Java Method
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The last names in Figure 19-1 may s
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Figure 19-2: Two objects, each with
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Chapter 19: Creating New Java Metho
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} void fillWithData() { Random myRa
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} void display() { NumberFormat cur
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Figure 19-6: Passing a value to a m
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Figure 19-7: Cbj’s account and Br
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In This Chapter Swinging into acti
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Figure 20-1: What a nice window! Mo
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Figure 20-4: The frame in Listing 2
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Taking Action The previous section
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Figure 20-6: A brandnew frame. Figu
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In This Chapter Chapter 21 Ten Sets
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Chapter 22 Ten Useful Classes in th
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Math Do you have any numbers to cru
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• Symbols • && (and operator),
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• C • Calling addInterest Metho
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File➪Open Workspace (JCreator), 3
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errors, diagnosing errors. See also
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input file creating, 222-223 naming
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enum type, 176 Faulty Password Chec
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pack, 352 parentheses and, 328 pars
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method and, 328 parameters and, 336
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testing code, 222-224 troubleshooti
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static, 320-323 String class, 305-3
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