Java Programming: A Simple Welcome Program and Compilation Process, Slides of Java Programming

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Advance Computer Programming^ Introduction to Java

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A Simple Java Program //This program prints Welcome to Java!public class Welcome {

public static void main(String[] args) {

System.out.println("Welcome to Java!"); } }

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Listing 1.

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Creating and Editing Using WordPad^ To use WordPad, type

write Welcome.java from the DOS prompt.

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Creating, Compiling, and Running Programs

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Source Code Create/Modify Source Code Compile Source Codei.e., javac Welcome.java

Bytecode Run Byteode i.e., java Welcome

Result

If compilation errors If runtime errors or incorrect result

public class Welcome {public static void main(String[] args) {

System.out.println("Welcome to Java!"); } } …Method Welcome()0 aload_0… Method void main(java.lang.String[])0 getstatic #2 …3 ldc #3 <String

"Welcome to

Java!

"> 5 invokevirtual #4 …8 return

Saved on the disk stored on the disk

Source code (developed by the programmer)Byte code (generated by the compiler for JVMto read and interpret, not for you to understand)

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Trace a Program Execution

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//This program prints Welcome to Java!public class Welcome {

public static void main(String[] args) {

System.out.println("Welcome to Java!"); } }

Execute statement

animation

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Trace a Program Execution

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//This program prints Welcome to Java!public class Welcome {

public static void main(String[] args) {

System.out.println("Welcome to Java!"); } } animation

print a message to theconsole

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Compiling and Running Java fromTextPad

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Compiling and Running Java fromJBuilder

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Anatomy of a Java Program • Comments• Package• Reserved words• Modifiers• Statements• Blocks• Classes• Methods• The main method

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Comments

In Java, comments are preceded by two slashes (//)in a line, or enclosed between /* and / in one ormultiple lines. When the compiler sees //, it ignoresall text after // in the same line. When it sees /, itscans for the next / and ignores any text between/ and */.

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Reserved Words

Reserved words or keywords are words that have aspecific meaning to the compiler and cannot be usedfor other purposes in the program. For example,when the compiler sees the word class, itunderstands that the word after class is the namefor the class. Other reserved words in Listing 1.1 arepublic, static, and void. Their use will be introducedlater.

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Modifiers Java uses certain reserved words called modifiersthat specify the properties of the data, methods,and classes and how they can be used. Examplesof modifiers are public and static. Othermodifiers are private, final, abstract, andprotected. A public datum, method, or class canbe accessed by other programs. A private dat ormethod cannot be accessed by other programs.

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Blocks

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A pair of braces in a program forms a block that groupscomponents of a program.

public class Test {

public static void main(String[] args) {

System.out.println("Welcome to Java!"); } }

Class block

Method block

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Classes

The class is the essential Java construct. A class is atemplate or blueprint for objects. To program inJava, you must understand classes and be able towrite and use them. For now, though, understandthat a program is defined by using one or moreclasses.

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