undefined | unit 3 java as object oriented programming language overview

PPL

Unit-3

Java as Object Oriented Programming Language Overview

Q1) Explain fundamentals of java

A1) Java programming language was originally developed by Sun Microsystems which was initiated by James Gosling and released in 1995 as core component of Sun Microsystems' Java platform (Java 1.0 [J2SE]).

The latest release of the Java Standard Edition is Java SE 8. With the advancement of Java and its widespread popularity, multiple configurations were built to suit various types of platforms. For example: J2EE for Enterprise Applications, J2ME for Mobile Applications.

The new J2 versions were renamed as Java SE, Java EE, and Java ME respectively. Java is guaranteed to be Write Once, Run Anywhere.

Java is −

Object Oriented− In Java, everything is an Object. Java can be easily extended since it is based on the Object model.

Platform Independent− Unlike many other programming languages including C and C++, when Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by the Virtual Machine (JVM) on whichever platform it is being run on.

Simple− Java is designed to be easy to learn. If you understand the basic concept of OOP Java, it would be easy to master.

Secure− With Java's secure feature it enables to develop virus-free, tamper-free systems. Authentication techniques are based on public-key encryption.

Architecture-neutral− Java compiler generates an architecture-neutral object file format, which makes the compiled code executable on many processors, with the presence of Java runtime system.

Portable− Being architecture-neutral and having no implementation dependent aspects of the specification makes Java portable. Compiler in Java is written in ANSI C with a clean portability boundary, which is a POSIX subset.

Robust− Java makes an effort to eliminate error prone situations by emphasizing mainly on compile time error checking and runtime checking.

Multithreaded− With Java's multithreaded feature it is possible to write programs that can perform many tasks simultaneously. This design feature allows the developers to construct interactive applications that can run smoothly.

Interpreted− Java byte code is translated on the fly to native machine instructions and is not stored anywhere. The development process is more rapid and analytical since the linking is an incremental and light-weight process.

High Performance− With the use of Just-In-Time compilers, Java enables high performance.

Distributed− Java is designed for the distributed environment of the internet.

Dynamic− Java is considered to be more dynamic than C or C++ since it is designed to adapt to an evolving environment. Java programs can carry extensive amount of run-time information that can be used to verify and resolve accesses to objects on run-time.

Q2) Explain history of java

A2) History of Java

James Gosling initiated Java language project in June 1991 for use in one of his many set-top box projects. The language, initially called ‘Oak’ after an oak tree that stood outside Gosling's office, also went by the name ‘Green’ and ended up later being renamed as Java, from a list of random words.

Sun released the first public implementation as Java 1.0 in 1995. It promised Write Once, Run Anywhere (WORA), providing no-cost run-times on popular platforms.

On 13 November, 2006, Sun released much of Java as free and open source software under the terms of the GNU General Public License (GPL).

On 8 May, 2007, Sun finished the process, making all of Java's core code free and open-source, aside from a small portion of code to which Sun did not hold the copyright.

Tools You Will Need

For performing the examples discussed in this tutorial, you will need a Pentium 200-MHz computer with a minimum of 64 MB of RAM (128 MB of RAM recommended).

You will also need the following softwares−

Linux 7.1 or Windows xp/7/8 operating system

Java JDK 8

Microsoft Notepad or any other text editor

Q3) Explain array in java

A3) Java array is an object which contains elements of a similar data type. Additionally, The elements of an array are stored in a contiguous memory location. It is a data structure where we store similar elements. We can store only a fixed set of elements in a Java array.

Array in Java is index-based, the first element of the array is stored at the 0th index, 2nd element is stored on 1st index and so on.

Unlike C/C++, we can get the length of the array using the length member. In C/C++, we need to use the sizeof operator.

In Java, array is an object of a dynamically generated class. Java array inherits the Object class, and implements the Serializable as well as Cloneable interfaces. We can store primitive values or objects in an array in Java. Like C/C++, we can also create single dimentional or multidimentional arrays in Java.

Moreover, Java provides the feature of anonymous arrays which is not available in C/C++.

Java array

Advantages

Code Optimization: It makes the code optimized, we can retrieve or sort the data efficiently.

Random access: We can get any data located at an index position.

Disadvantages

Size Limit: We can store only the fixed size of elements in the array. It doesn't grow its size at runtime. To solve this problem, collection framework is used in Java which grows automatically.

Q4) Write an Example of Java Array

A4) Let's see the simple example of java array, where we are going to declare, instantiate, initialize and traverse an array.

//Java Program to illustrate how to declare, instantiate, initialize

//and traverse the Java array.

class Testarray{

public static void main(String args[]){

int a[]=new int[5];//declaration and instantiation

a[0]=10;//initialization

a[1]=20;

a[2]=70;

a[3]=40;

a[4]=50;

//traversing array

for(int i=0;i<a.length;i++)//length is the property of array

System.out.println(a[i]);

}}

Output:

Q5) Explain multidimensional array in java

A5) Multidimensional Array in Java

In such case, data is stored in row and column based index (also known as matrix form).

Syntax to Declare Multidimensional Array in Java

dataType[][] arrayRefVar; (or)

dataType [][]arrayRefVar; (or)

dataType arrayRefVar[][]; (or)

dataType []arrayRefVar[];

Example to instantiate Multidimensional Array in Java

int[][] arr=new int[3][3];//3 row and 3 column

Example to initialize Multidimensional Array in Java

arr[0][0]=1;

arr[0][1]=2;

arr[0][2]=3;

arr[1][0]=4;

arr[1][1]=5;

arr[1][2]=6;

arr[2][0]=7;

arr[2][1]=8;

arr[2][2]=9;

Example of Multidimensional Java Array

Let's see the simple example to declare, instantiate, initialize and print the 2Dimensional array.

//Java Program to illustrate the use of multidimensional array

class Testarray3{

public static void main(String args[]){

//declaring and initializing 2D array

int arr[][]={{1,2,3},{2,4,5},{4,4,5}};

//printing 2D array

for(int i=0;i<3;i++){

for(int j=0;j<3;j++){

System.out.print(arr[i][j]+" ");

}

System.out.println();

}

}}

Output:

1 2 3

2 4 5

4 4 5

Q6) What is the class name of Java array?

A6) In Java, an array is an object. For array object, a proxy class is created whose name can be obtained by getClass().getName() method on the object.

//Java Program to get the class name of array in Java

class Testarray4{

public static void main(String args[]){

//declaration and initialization of array

int arr[]={4,4,5};

//getting the class name of Java array

Class c=arr.getClass();

String name=c.getName();

//printing the class name of Java array

System.out.println(name);

}}

Output:

Copying a Java Array

We can copy an array to another by the arraycopy() method of System class.

Syntax of arraycopy method

public static void arraycopy(

Object src, int srcPos,Object dest, int destPos, int length

)

Q7) What is cloning an array in java?

A7) Cloning an Array in Java

Since, Java array implements the Cloneable interface, we can create the clone of the Java array. If we create the clone of a single-dimensional array, it creates the deep copy of the Java array. It means, it will copy the actual value. But, if we create the clone of a multidimensional array, it creates the shallow copy of the Java array which means it copies the references.

//Java Program to clone the array

class Testarray1{

public static void main(String args[]){

int arr[]={33,3,4,5};

System.out.println("Printing original array:");

for(int i:arr)

System.out.println(i);

System.out.println("Printing clone of the array:");

int carr[]=arr.clone();

for(int i:carr)

System.out.println(i);

System.out.println("Are both equal?");

System.out.println(arr==carr);

}}

Output:

Printing original array:

Printing clone of the array:

Are both equal?

false

Q8) Explain String Handling: String class methods

A8) In Java, string is basically an object that represents sequence of char values. An array of characters works same as Java string. For example:

char[] ch={'j','a','v','a','t','p','o','i','n','t'};

String s=new String(ch);

is same as:

String s="javatpoint";

Java String class provides a lot of methods to perform operations on strings such as compare(), concat(), equals(), split(), length(), replace(), compareTo(), intern(), substring() etc.

The java.lang.String class implements Serializable, Comparable and CharSequence interfaces.

String in Java

CharSequence Interface

The CharSequence interface is used to represent the sequence of characters. String, StringBuffer and StringBuilder classes implement it. It means, we can create strings in java by using these three classes.

CharSequence in Java

The Java String is immutable which means it cannot be changed. Whenever we change any string, a new instance is created. For mutable strings, you can use StringBuffer and StringBuilder classes.

We will discuss immutable string later. Let's first understand what is String in Java and how to create the String object.

What is String in java

Generally, String is a sequence of characters. But in Java, string is an object that represents a sequence of characters. The java.lang.String class is used to create a string object.

How to create a string object?

There are two ways to create String object:

By string literal

By new keyword

1) String Literal

Java String literal is created by using double quotes. For Example:

String s="welcome";

Each time you create a string literal, the JVM checks the "string constant pool" first. If the string already exists in the pool, a reference to the pooled instance is returned. If the string doesn't exist in the pool, a new string instance is created and placed in the pool. For example:

String s1="Welcome";

String s2="Welcome";//It doesn't create a new instance

Java string literal

In the above example, only one object will be created. Firstly, JVM will not find any string object with the value "Welcome" in string constant pool, that is why it will create a new object. After that it will find the string with the value "Welcome" in the pool, it will not create a new object but will return the reference to the same instance.

Note: String objects are stored in a special memory area known as the "string constant pool".

Q9) Why Java uses the concept of String literal?

A9) To make Java more memory efficient (because no new objects are created if it exists already in the string constant pool).

2) By new keyword

String s=new String("Welcome");//creates two objects and one reference variable

In such case, JVM will create a new string object in normal (non-pool) heap memory, and the literal "Welcome" will be placed in the string constant pool. The variable s will refer to the object in a heap (non-pool).

Java String Example

public class StringExample{

public static void main(String args[]){

String s1="java";//creating string by java string literal

char ch[]={'s','t','r','i','n','g','s'};

String s2=new String(ch);//converting char array to string

String s3=new String("example");//creating java string by new keyword

System.out.println(s1);

System.out.println(s2);

System.out.println(s3);

}}

java

strings

example

Q10) Write an example of Object and Class: Initialization through reference

A10) Initializing an object means storing data into the object. Let's see a simple example where we are going to initialize the object through a reference variable.

File: TestStudent2.java

class Student{

int id;

String name;

}

class TestStudent2{

public static void main(String args[]){

Student s1=new Student();

s1.id=101;

s1.name="Sonoo";

System.out.println(s1.id+" "+s1.name);//printing members with a white space

}

Output:

101 Sonoo

We can also create multiple objects and store information in it through reference variable.

File: TestStudent3.java

class Student{

int id;

String name;

}

class TestStudent3{

public static void main(String args[]){

//Creating objects

Student s1=new Student();

Student s2=new Student();

//Initializing objects

s1.id=101;

s1.name="Sonoo";

s2.id=102;

s2.name="Amit";

//Printing data

System.out.println(s1.id+" "+s1.name);

System.out.println(s2.id+" "+s2.name);

}

Output:

101 Sonoo

102 Amit

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