Advanced Programming Collage of Information Technology University of Palestine, Gaza Prepared by: Mahmoud Rafeek Alfarra Lecture 2: Major Concepts of Programming

2 Outlines Java: Overview  Java: Overview  Java Virtual Machine (JVM)  The Java runtime environment  Variables Types  Statements  Selection  Iteration  Garbage collection

3 Overview  Java is a programming language originally developed by Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform.  The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities.  Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of computer architecture.

4 Java Virtual Machine (JVM)  A Java Virtual Machine (JVM) is a set of computer software programs and data structures which use a virtual machine model for the execution of other computer programs and scripts.  JVMs operate on Java bytecode, which is normally (but not necessarily) generated from Java source code; a JVM can also be used to implement programming languages other than Java.

5 Java Virtual Machine (JVM)  One characteristic of Java is platform independence, which means that programs written in the Java language must run similarly on any supported hardware/operating-system platform. One should be able to write a program once, compile it once, and run it anywhere.

6 The Java runtime environment

7 Variables Types  Java data types fall into two categories. Primitive types 1. Primitive types represent simple values that have built-in functionality in the language; they are fixed elements, such as literal constants and numbers. Reference types 2. Reference types (or class types) include objects and arrays; they are called reference types because they "refer to" a large data type which is passed "by reference," as we'll explain shortly.

8 Primitive Types  Numbers, characters, and Boolean values are fundamental elements in Java.

9 Primitive Types  Variable declaration and initialization: 1 2 3

10 Reference Types  Complex data types (user defined) from simple primitives by creating a class. Each class then serves as a new type in the language.  For example,  if we create a new class called Foo in Java,  A new type called Foo is created.  The type of an item governs how it's used and where it can be assigned.

11 Statements  Statements and expressions in Java appear within a code block. Statements Selection Iteration Sequential

12 Selection  The if structure  Causes the program to make a selection  Chooses based on conditional  Any expression that evaluates to a bool type  True: perform an action  False: skip the action  Single entry/exit point  Require no semicolon in syntax print “Passed” Grade >= 60 true false

13 Selection Grade >= 60 print “Passed”print “Failed” falsetrue Another types, study them

14 Selection

15 Iteration  Repetition Structure  An action is to be repeated  Continues while statement is true  Ends when statement is false  Contain either a line or a body of code  Must alter conditional  Endless loop

16 Iteration  while Repetition Structure true false Product = 2 * product Product <= 1000

17 Iteration true false action(s) condition do/while Repetition Structure

18 Iteration counter++ Establish initial value of control variable. Determine if final value of control variable has been reached. counter <= 10 Console.WriteLine ( counter * 10 ); true false int counter = 1 Body of loop (this may be multiple statements) Increment the control variable. For Repetition Structure

19 Garbage collection  Java uses an automatic garbage collector to manage memory in the object lifecycle.  The programmer determines when objects are created, and the Java runtime is responsible for recovering the memory once objects are no longer in use.  Once no references to an object remain, the unreachable object becomes eligible to be freed automatically by the garbage collector.

20 Next Lecture isa Arrays and Concepts of OOP