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Creating Your First Computer Program in Java Margaret Yau Impacts of Software The Internet WWW - over 109.9 million active websites - estimated 1.5 billion Internet users (~ 5 x U.S. Population) - 14.3 billion searches by Americans in May 09 - Microsoft: the world’s largest software company - company worth $36 billion (2008) - over 400 million copies of Windows XP sold - the largest social networking site - company worth $3.75 – 5 billion - more than 200 million active users - over 21 million iPhones sold - 50,000 applications available for download Can you even imagine a day without using software? Computer programming is fun and powerful And it is not just for nerds "I'm not coming down for dinner, didn't you read my blog ?!?!" Creating Your First Program in • Java – High-level – Object-oriented programming (OOP) language – Platform-independent – Free and open-source Three Important Parts of Computer Programming • Coding • Compiling • Testing 1. Coding • Source Code: collection of statements or declarations written in some human-readable computer programming language • A high-level way of communicating with the computer English: Print the string “How are you?” to the computer screen. Java: System.out.println(“How are you?"); Coding Your “Hello World!” Java Program Define a type of object (class) Class name class Hello { Define the main behavior (method) public static void main ( String[] args ) { System.out.println("Hello World!"); } } A statement that prints “Hello World!” to the main output device <class name>.java 2. Compiling • A compiler translates source code in a highlevel language to code in a low-level language that a particular type of machines understands (often binary form) Source code (Hello.java) class Hello { public static void main { System.out.println… Compiler (javac) Object code (Java bytecodes: Hello.class) 10001010 01010011 11110101 10010101 01010011 11110101 10010101 10010101 Compiling Your Java Program javac <source file name> Hello.java javac Source Code Compiler Hello.class Object Code 3. Testing • Execute the program Processor Object code Machine • Find software bugs (error, mistake, or failure) • Verify that the program meets its requirements 3. Testing • Execute the program • Find software bugs (error, mistake, or failure) • Verify that the program meets its requirements Executing (Running) Your Java Program java <class name> Yay! I ran my first Java program! You have coded, compiled, and tested your first computer program in Java. What’s Next • Software can be designed to perform almost anything computable. • Observe and ask what people need, and use your imagination… e.g. program - that really understands natural language - that computes one quadrillion (1015) digits of π - that reads your mind - that creates original and artistic songs and poetry And you may be the next … Bill Gates Microsoft Steve Jobs Apple Larry Page Sergey Brin Google Mark Zuckerberg Facebook Questions?