Arrays, References, Memory Leaks

•                      Arrays are references! 

•                      Garbage collection reclaims arrays that can not be accessed! 

•                      References are initialized to null 

•                      When done with a reference set it to null 

public classArrayExamples{public static void main( String args[] )

{int[] integerArray = new int[ 4 ];integerArray[ 1 ] = 12integerArray = new int[ 2 ]; // Memory Leak - No!integerArray[  1  ]  =  5;int[] aliasForArray = integerArray;aliasForArray[  1  ]  =  10;System.out.println( integerArray[ 1 ] ); //Prints 10}

}

HEAP ALLOCATION

integerArray[ 1 ] = 12

integerArray = new int[ 2 ]; // Memory Leak - No!

integerArray[  1  ]  =  5;

int[] aliasForArray = integerArray;

aliasForArray[  1  ]  =  10;

Memory Problems in C/C++

Memory Leaks

Memory that program has allocated but can no longer access  int* trouble = new int( 5 );

Arrays

Major differences with C/C++ arrays:
• Java arrays are references
• Java arrays know their size
• Java checks the bounds of an array when accessed
• Java multidimensional arrays need not be rectangular
• Java array elements are initialized

Example 1:)
public class SimpleReferenceExample{public static void main( String args[] )
{// Reference allocated, no array space allocatedfloat[] sampleArray;//allocate array locations on heapsampleArray = new float[ 12 ];// Indexing starts at 0 like C/C++sampleArray[ 0 ] = 3.2F;int[] integerArray = new int[ 3 ];
// Reference refers to new array.// Old array available for garbage collectionsampleArray = new float[ 2 ];}
} Example 2:)
public class ArrayExamples{public static void main( String args[] )
{// Two locations to place [ ]int integerArray[ ];int[ ] alias;integerArray = new int[ 10 ]; // Indexed from 0 to 9// Note use of .length to get array sizefor ( int index = 0; index < integerArray.length; index++ )
integerArray[  index  ]  =  5;alias = integerArray; // Arrays are referencesalias[  3  ]  =  10;System.out.println( integerArray[ 3 ] ); //Prints 10
integerArray = new int[ 8 ];System.out.println( integerArray[ 3 ] ); //Prints 0, Why?System.out.println( alias[ 3 ] ); //Prints 10System.out.println( integerArray ); //Prints [I@5e300868}}

Casting

class Casting{public static void main( String args[] )

{int anInt = 5;float aFloat = 5.8f;aFloat = anInt; // Implicit casts up are okanInt = aFloat ; // Compile error,

// must explicitly cast downanInt = (int) aFloat ;float error = 5.8; // Compile error, 5.8 is doublefloat works = ( float) 5.8;char c = (char) aFloat;double aDouble = 12D;double bDouble = anInt + aDouble; // anInt is cast upto double,int noWay = 5 / 0; // Compile error, compiler detects

// zero divideint zero = 0;int trouble = 5 / zero; //Some compilers may give error hereint notZeroYet;notZeroYet = 0;

 trouble = 5 / notZeroYet ; // No compile error!}}

Ints and Booleans are Different

class UseBoolean {public static void main( String args[] )

{if ( ( 5 > 4 ) == true )System.out.println( "Java's explicit compare " );if ( 5 > 4 )System.out.println( "Java's implicit compare " );if ( ( 5 > 4 ) != 0 ) // Compile errorSystem.out.println( "C way does not work" );boolean cantCastFromIntToBoolean = (boolean) 0;

// compile errorint  x  =  10;int  y  =  5;if ( x = y ) // Compile error

System.out.println( "This does not work in Java " );}} 

Basic Data Types

class PrimitiveTypes{public static void main( String args[] )
{// Integral Typesbyte aByteVariable; // 8-bitsshort aShortVariable; // 16-bitsint aIntVariable; // 32-bitslong aLongVariable; // 64-bits// Floating-Point Typesfloat aFloatVariable; // 32-bit IEEE 754 floatdouble aDoubleVariable; // 64-bit IEEE 754 float// Character Typechar aCharVariable; // always 16-bit Unicode// Boolean Typesboolean aBooleanVariable; // true or false}}
Operations on Primitive Types

class Operations{public static void main( String args[] )
{int a = 2;int b = +4;int c = a + b;if ( b > a )
System.out.println("b is larger");else
System.out.println("a is larger");System.out.println( a << 1); // Shift left: 4System.out.println( a >> 1); // Shift right: 1System.out.println( ~a ); // bitwise negation: -3System.out.println( a | b); // bitwise OR: 6System.out.println( a ^ b); // bitwise XOR: 6System.out.println( a & b); // bit

Guide to JAVA

CLASSPATH
Java uses the environment variable CLASSPATH to locate class libraries
• .class files those needed to compile or run the program it searches from
CLASSPATH
• By default class path consists only the current directory but you can provide them in –classpath option of javac or include directories in CLASSPATH environment variables.
• Example classpath = . ; c:\java\lib; c:\csi211\lab


Some Basic Java Syntax
Java Comments
/* Standard C comment works  */
// C++ comment works
/** Special comment for documentation – java comments */
class Syntax
{ public static void main( String args[] ){
int aVariable = 5;double aFloat = 5.8;
if ( aVariable < aFloat )System.out.println( "True" );
int b = 10; // This is legal in Javachar c;c = 'a';
}}
Java Program Style and Layout
• Three different indentation styles you can use
• You can pick a reasonable indentation style and use it consistently in your programs

Style#1
class Syntax { // brace starts from here
public static void main( String args[] ) {int aVariable = 5;if ( aVariable < aFloat )
System.out.println( "True" );}}
Style #2
class Syntax
{ // brace startspublic static void main( String args[] ){
int aVariable = 5;if ( aVariable < aFloat )System.out.println( "True" );}}
Style#3
class Syntax{// brace startspublic static void main( String args[] )
{int aVariable = 5;if ( aVariable < aFloat )
System.out.println( "True" );}}
Naming conventions
Class Naming Uses Capitalized word(s) i.e. Title case
Examples:-   HelloWorld, MyList, StudentMark
Wrong: helloWorld,  HW (do not use abbreviat

An Example HelloWorld

/**    This is my first java program */
public class HelloWorldExample
{ public static void main( String args[] ){
System.out.println("Hello World");}}

Java Source Code Naming Conventions
• All java source file should end in .java
• Each .java file can contain only one public class
• The name of the file should be the name of the public class plus ".java"
• Do not use abbreviations in the name of the class
• If the class name contains multiple words then capitalize the first letter of each word ex. HelloWorld.java

Java - The Platform

• Java has a large API (application programming interface) covering a wide range of areas The following list of Java APIs and applications from Sun show the range of applications of Java . For reference http://java.sun.com/products/index.html
• Java Foundation Classes (JFC) - GUI
• JDBC Database Access
• JavaBeans - componentware
• Java Web Server
• EmbeddedJava - Java on embedded devices


JAVA IDE
Using JDK you can compile and run java program from command line.
 javac HelloWorld. java  - compiling here and it will produce HelloWorld.class i.e. bytecode.
java HelloWorld  - It runs java byte code on native machine
Creating, Compiling, Debugging and Execution for these four steps JDK is not user friendly. IDE is provided for that. A list of IDEs are:
 Eclipse  - from IBM
 Netbeans.

United International University Course Outline

Trimester: Spring 2013
Course: CSI 211
Course Title: Object-oriented Programming
Faculty: Md. Faisal Kabir
Email: faisal@cse.uiu.ac.bd
Assessment:
Component Marks(%)
Attendance 5
Continuous Assessment - Class test 10
Continuous Assessment - Assignment 15
Midterm Examination 30
Final Examination 40
Total 100
Reference Book
• The Complete Reference Herbert Schieldt Java 2.0
• The Java Programming, Deitel and Deitel
This document is prepared by : Dr. S M Monzurur Rahman, Professor, dept. of CSE,UIU
Week 1
Lecture 1
Fundamental of Programming; Java Introduction; Basic Java Syntax: IO
Basic Data Types, Primitive Type Ranges, Operations on Primitive Types, NaN
and Infinity, Casting Default Values of Variables.
Lecture 2
Arrays; Multidimensional Arrays; Some JDK Array Features; Strings: Strings are
Constant!, Strings Reading Command Line Arguments; Control Structures; Jump
Statements; Methods (Functions); Final Variables.
Week 2
Lecture 1
Classes: Fields, Methods; Initializing Fields; Direct Assignment; Instance
Initialization Blocks; Constructors; Overloading Methods; this ;Finalize; Access
Levels for Fields and Methods; Class Names, Packages, Import, CLASSPATH.
Lecture 2
Class members; variables References ; Static, recursion.
• Class Test -1
2
Week 3
Lecture 1
Object oriented concept, Information hiding; examples.
Lecture 2
Inheritance; Class Object; Inheritance and Name Clashes; Super; Constructors
and Inheritance; Static Methods; Access Levels and Inheritance; Inheritance and
Final; Abstract Classes; Relationships between Classes: Is-kind-of, is-a, is-a-typeof
is-analogous-to is-part-of or has-a.
Week 4
Lecture 1
Class Test -2
Interfaces; Clone; Abstract method; Abstract method vs interfaces.
Lecture 2
Java collections.
Week 5
Lecture 1
Exceptions Handling; Java IO
Lecture 2
Nested and Inner Classes.
Week 6
Mid Exam
Week 7
Lecture 1
Threads;
Lecture 2
Generics
Week 8
Lecture 1
Problem Solving – Class Participation (no lecture notes)
Lecture 2
Serialization; Making an Object Serializable; Serializable objects can contain
other objects; Saving and Recovering; Non-Serializable Fields – transient;
Customizing Deserialization; Customizing Serialization; Class Versions; Serial
version.
3
Week 9
Lecture 1
Class Test -3
Internationalization;
Lecture 2
Java Foundation Classes, Java Graphics.
Week 10
Lecture 1
Layouts: Flow layout, Grid layout, border lay out card layout
Events, Event Handling, Containers.
Lecture 2
Class Participation (Problems will be given and solutions will be asked to students,
Class Test-4 equivalent)
Week 11
Lecture 1
GUI Components
Lecture 2
Applet;
Week 12
Lecture 1
More about applets
Lecture 2
Class Test -4
A variety of examples on Applets part1
Week 13
Lecture 1
Architecture Design Pattern; Model-View in Java.
Lecture 2
• Summarization
END OF SEMESTER!!! ENJOY!!!