Spring 2009 Programming Fundamentals I Java Programming XuanTung Hoang Lecture No. 8

Review

XuanTung Hoang 3 Introduction to Computers Computer :  Hardware 6 logical units: Input, output, CPU, ALU, memory, secondary storage  Software: Computer programs that command computer hardware to for solving computing tasks Programming languages: For writing computer software  Machine language  assembly language  High-level languages  High level language needs translator or compiler

XuanTung Hoang 4 Java Programming Language A high level language  Use both interpreter and compiler Compiler: Source code  byte code Interpreter: byte code  machine language J2SE Java Platform  JRE – Java Runtime Environment: Java Virtual Machine (JVM): interpreter, java.exe Libraries  JDK – Java Development Kits JRE Compiler: javac.exe Library + other tools

XuanTung Hoang 5 Java Language: Things to remember Java is case-sensitive Statements end with “ ; ” Comments: //, /* … */ Block of code: { … } Array: [ ] Keywords: class, this, public, private, static, final, int, double, float, short, long, boolean, true, false, if, for, while, do, switch, case, break, continue, new, return, …

XuanTung Hoang 6 Java Language: Things to remember One file = one class  File name = class name Compile: javac Run: java Identifiers (class/method/variable name):  Comprise of: lower case chars (a – z), upper-case char ( A – Z), numeric char (0 – 9), _ int number_Of_people1 = 0; // valid int = 5; // invalid

XuanTung Hoang 7 Java Language: Important concepts Data type:  Primitive data type: int, short, long, float, double, boolean, char, byte Built-int data type  class (object/reference): Provided by class libraries (E.g.: String) or made by users Object: instance of a class  Created with new  Accessed through reference Using “.”

XuanTung Hoang 8 Java Language: Important concepts Variable:  4 properties: Name: identifier Type: Primitive data type or reference (class, object reference) Size: depends on type Value: specific value in a certain context  Two type of variables Instance variable: member of a class  Non-static instance variable is associated with a specific object  Static instance variable is associated with a class (do not need a specific object) Local variable  Declaration and initialization Non-static instance variable can ONLY be initialized in constructor  Scope of a variable Variable can be shadowed by other variable (with the same name)

XuanTung Hoang 9 Java Language: Important concepts Class:  Instance variables Static/non-static Constants: define with final  Methods Static/non-static 3 ways to call a methods Static methods cannot “directly call” non-static methods Return type and return expression agreement Constructors: special method for initializing object’s instance variabl es (no return type, name = class name) Get/set methods Why main method should be static?

XuanTung Hoang 10 Java Language: Operator Arithmetic: +, -, *, /, %, ++, --, +=, -=, *=, /=, %=  For integers  For floating point numbers Relational: >, =, <=, ==, !=  Be careful when using = = with floating point numbers Logical: &, &&, |, ||, ^^, !  !(2 >4)  (3 3)) new operator

XuanTung Hoang 11 Java language: Control statements if, if … else switch … case  Only for integer expression for, while, do … while  Empty statement can be allowed Be careful when putting “;”  if( x < 2) ; { … }  for (int k ; k < 10; k++) ; { … }  …

XuanTung Hoang 12 Arrays Declaration / creation / initialization Array of primitive type Array of object references  When an array of references is created, each element of the array will be a reference that is pointing to null Multi dimensional array  Array of arrays