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Introduction to Java IB Computer Science II Paul Bui What does a computer look like? Central Processing Unit (CPU) Memory What is a computer program? 1010111101010101001100100000111 0101101011110101010100110010000 0111010101111010101010011001000 0011101010111101010101001100100 0001110101011110101010100110010 0000111010101111010101010011001 0000011101010111101010101001100 1000001110101011110101010100110 0100010010000011101010111101010 Assembly Language Also known as machine code/language or low-level language Example: ADD R1, R2, R3 SUB R1, R1, 1 MULT R3, R1, R2 Why can’t I run my PC programs on a Mac?!?!? Different from machine to machine I Hate Tedious Stuff Old school programs Invention of the high-level language ADD R1, R2, R3 SUB R1, R1, 1 MULT R4, R1, R2 D = B*(B+C-1) Waaaay easier to understand Compilers Translates or converts a high-level language (e.g., Java, C++) to a lowlevel language Does other stuff too! Checks syntax Optimizations and more! One would say, “Yeah, so I compiled my code to an executable or binary” Before Java… Applications or Programs Operating System (Windows XP, Mac OSX, etc.) Hardware (CPU + Memory + etc.) How Java Works Java Application or Java Program Java Runtime Environment or Java Virtual Machine Operating System (Windows XP, Mac OSX, etc.) Hardware (CPU + Memory + etc.) What does this mean? Java bytecode (Java’s low-level language) Java sourcecode (high-level) Java bytecode (low-level) assembly Two different operating systems with the JRE or JVM can run the same Java program Ok, so I want to program now! //My first Java program! class HelloWorld{ public static void main(String[] args) { System.out.println("Hello World!"); } } How to Compile and Execute 1) 2) 3) Open a text editor (gedit, tea, vi, etc.) Code Code Code Save file as CLASSNAME.java Example: HelloWorld.java 4) 5) 6) Open a terminal javac HelloWorld.java java HelloWorld