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The Java Programming Language • Invented 1995 by James Gosling at Sun Microsystems. • Based on previous languages: C, C++, Objective-C, … • Intended to be a safe programming language for the Internet • Common choice for first programming language Object oriented Encourages good programming habits Very popular commercially Simpler and more elegant than C++, but similar to it Cool Lecture A Slide 1 of 40. Hello World Program // My First Program!! public class HelloWorld { public static void main(String[] args){ System.out.println(“Hello World!”); } } Lecture A Slide 2 of 40. Java Program Elements • Words Keywords Identifiers • Constants Numbers Strings • Symbols ()[]{},.;+-*/ • Comments Lecture A Slide 3 of 40. Java Elements Comment Identifier Symbols // My First Program!! public class HelloWorld { public static void main(String[] args){ System.out.println(“Hello World!”); } } Keywords String Constant Lecture A Slide 4 of 40. Java Program Structure • A program is composed of a collection of classes • Each class contains a collection of methods • Each method is composed of a sequence of instructions (commands, statements) Lecture A Slide 5 of 40. Java Program Structure Class Method // My First Program!! public class HelloWorld { public static void main(String[] args){ System.out.println(“Hello World!”); } } Instruction Lecture A Slide 6 of 40. Running a Java Program • Use an editor to enter (type) the program Save to a file named HelloWorld.java • Use the compiler to translate the program into bytecode javac HelloWorld.java This produces a file named HelloWorld.class • Run the program using the Interpreter java HelloWorld Lecture A Slide 7 of 40. Java Compilation Xxx.java Compiler Xxx.class Interpreter Output Lecture A Slide 8 of 40. Entering a Java Program into an Editor Lecture A Slide 9 of 40. Running a Java Program Lecture A Slide 10 of 40.