JAVA Basics Presentation for introduction to JAVA programming languauge

Java - Overview
Basics of Java

Introduction of Java
• Java is one of the powerful general-purpose programming languages, created
in 1995 by Sun Microsystems (now owned by Oracle).
• Java is Object-Oriented.
• Syntax of Java is similar to C/C++ but doesn’t allow low level
programming functionality like pointers.
• Java code is always written in the form of classes and objects. Android
heavily relies on the Java programming language all the
• SDKs required to build for Android applications use the standard
libraries of Java.

Features of Java
Java is a simple language:
• Syntax is similar to C++.
• It has excluded some features like explicit pointers and operator
overloading.
• It has provided the garbage collector for memory management. It
helps in automatically delete unused objects.
Java is a multi-threaded language:
• Java can perform many tasks at once by defining multiple
threads.
• For example, a program that manages a Graphical User
Interface (GUI) while waiting for input from a network
connection uses another thread to perform and waits instead
of using the default GUI thread for both tasks. This keeps the
GUI responsive.

Features of Java
Java is an object-oriented programming language.
Java is a platform-independent language:
• The programs written in Java language, after compilation, are
converted into an intermediate-level language called the bytecode,
which is a part of the Java platform irrespective of the machine on
which the programs run.
• This makes Java highly portable as its bytecodes can be run on any
machine by an interpreter called the Java Virtual Machine(JVM), and
thus, java provides ‘reusability of code’.

Identifiers in Java
Identifiers: Identifiers in Java are symbolic namesused for identification.
They can be a class name, variable name, method name, package name, constant
name, and more.

Identifiers in Java
All the marked section of the above code snippet is a type of identifier.
They are described as:
1 HelloJava (Class name),
2 main (main method),
3 String (Predefined Class name),
4 args (String variables),
5 System (Predefined class),
6 out (Variable name), and
7 println (method).

Data types specify the different sizes and values that can be stored in the variable.
There are two types of data types in Java:
1
1. Primitive data types: The primitive data types include boolean,
char, byte, short, int, long, float and double.
2. Non-primitive data types: The non-primitive data types include
Classes, Interfaces, and Arrays.
Data Types in Java

Data Types in Java
Figure 1: List of different datatypes

Boolean Type
A boolean data type can store either True or False.
Figure 2: Example illustrating boolean datatype
Figure 3: Output of the above code

Character Type
The char data type stores a single character.
Figure 4: Example illustrating char datatype

Integer
Type
An integer type stores an integer number with no fractional or decimal places.
Java has four integer types – byte, short, int, and long.
Figure 6: Example illustrating integer datatype

Integer
Type
Figure 7: Output of the above
code

Float Type
Floating-point is used for expressions involving fractional precision. It has two
types: float and double.
Figure 8: Example illustrating float datatype

Arrays
In Java, Array is a group of like-typed variables referred to by a common name.
Arrays in Java work differently than they do in C/C++. Following aresome
important points about Java arrays.
1. In Java, all arrays are dynamically allocated. Arrays may be stored in
contiguous memory.
2. Since arrays are objects in Java, we can find their length using the object
property length. This is different from C/C++, where we find length using
sizeof.
3. A Java array variable can also be declared like other variables with [] after
the data type.
4. The variables in the array are ordered, and eachhas an index beginning with
0.
5. Java array can also be used as a static field, a local variable, or a method
parameter.

Creating, Initializing, and Accessing an Arrays
One-Dimensional Arrays
Syntax to declare an array
 dataType var-name[];
 dataType[] var-name;
Instantiation of an Array in
Java
arrayRefVar=new
datatype[size];
• Multidimensional Array
Syntax to declare multi-
dimensional array
 dataType[][] arrayRefVar;
 dataType arrayRefVar[][];
Instantiation of a multi-dimensional
array in Java

Example of 1-D Array
Figure 10: 1-D array code
Figure 11: Output of the above c ode

Figure 12: 2-D array
code

Figure 13: Output of the above
code

ArrayIndexOutOfBoundsException
The Java Virtual Machine (JVM) throws an
ArrayIndexOutOfBoundsException if length of the array in negative, equal to the
array size or greater than the array size while traversing the array.
Figure 14: Erroneous code

Decision Making Statements
in Java

if-else Statements
A programming language uses control statements to control the flow of
execution of a program based on certain conditions.
These areused to cause the flow of execution to advance and branch based on
changes to the state of a program.
• if statement: It is used to decide whether a certain statement or block of
statements will beexecutedor not depending on certain conditions.
• else if statement: It is similar to if statement. It is usedwhen we want to put
more than on condition.
• else statement: It comes at the end of the if-else-if ladder. It will run
when none of the conditions is true.

if-else Statement
Figure 16: Basic structure of if-else-if statements

if-else Statement
Figure 17: Output will be 20 in the above case

Loops in Java
Looping in programming languages is a feature that facilitates the
execution of a set of instructions/functions repeatedly while some
condition evaluates to true.
Java provides 3 types of loops.
1. while: A while loop is a control flow statement that allows code to be
executed repeatedly based on a given Boolean condition. The while
loop can be thought of as a repeating if statement.
2. for: Unlike a while loop, a for statement consumes the initialization,
condition and increment/decrement in one line.
3. do while: do while loop is similar to a while loop with the only
difference that it checks for the conditions after executing the
statements once.

while Loop
Figure 18: Simple example displaying function of while loop

while Loop
Figure 19: Output for the above case (Same for and do-while, which is coming in the next slides)

for Loop
Figure 20: Simple example displaying function of for loop

do while Loop
Figure 21: Simple example displaying function of do while loop

for-each Loop
For-each is another array traversing technique like for loop, while loop, do-
while loop introduced in Java5.
Figure 22: Simple example displaying function of for each loop
Figure 23: Output for the above for-each loop code

Type conversion in Java
An overview

Type Conversion
When we assign a value of one data type to another, the two types might not be
compatible with each other. If the data types are compatible, then Java will
perform the conversion automatically, known asAutomatic Type Conversion, and
if not, then they need to be cast or converted explicitly. For example, assigning an
int value to a long variable.
Widening or Automatic Type Conversion: Widening conversion occurs when
two data types are automatically converted. This happens when:
• The two data types are compatible.
• When we assign a value of a smaller data type to a bigger data type.
Narrowing or Explicit Conversion: If we want to assign a value of a larger data
type to a smaller data type, we perform explicit type casting or narrowing.
• This is useful for incompatible data types where automatic conversion
cannot be done.
• Here, the target type specifies the desired type to convert the specified
value to.

Introduction of String
The string is a sequence of characters. In Java, objects of String are immutable
which means a constant and cannot be changed once created.
Creating a String: There are two ways to create a string in Java.
String literal
String s = “GeeksforGeeks”;
Using new keyword
String s = new String (“GeeksforGeeks”);

String’s Method in Java
int length()
Returns the number of characters in the String.
“GeeksforGeeks”.length(); // returns 13
Char charAt(int i)
Returns the character at ith index.
“GeeksforGeeks”.charAt(3); // returns ‘k’
String substring (int i)
Return the substring from the ith index character to end.
“GeeksforGeeks”.substring(3); // returns “ksforGeeks”
String substring (int i, int j)
Returns the substring from i to j-1 index.
“GeeksforGeeks”.substring(2, 5); // returns “eks”

String’s Method in Java
String concat( String str)
1Concatenates specified string to the end of this string.
2String s1 = ”Geeks”;
String s2 = ”forGeeks”;
String output =
s1.concat(s2); // returns
“GeeksforGeeks”
int indexOf (String s)
Returns the index within the string of the first occurrence of the
specified string.
String s = ”Learn Share Learn”;
int output = s.indexOf(“Share”); // returns 6
int indexOf (String s, int i)
Returns the index within the string of the first occurrence of the
specified string, starting at the specified index.
String s = ”Learn Share Learn”;
int output = s.indexOf(”ea”,3);// returns 13

Exception Handling in Java
An
overview

Exception Handling in Java
The Exception Handling in Java is one of the powerful mechanism to handle the
runtime errors so that the normal flow of the application can be maintained.
What is Exception in Java?
In Java, an exception is an event that disrupts the normal flow of the
program. It is an object which is thrown at runtime.
What is Exception Handling?
Exception Handling is a mechanism to handle runtime errors such as
ClassNotFoundException, IOException, SQLException,
RemoteException, etc.
Advantage of Exception Handling
The core advantage of exception handling is to maintain the normal flow
of the application. An exception normally disrupts the normal flow of the
application; that is why we need to handle exceptions.

Hierarchy of Java Exception Classes
The java.lang.Throwable class is the root class of Java Exception hierarchy
inherited by two subclasses: Exception and Error. The hierarchy of Java
Exception classes is given below:

Hierarchy of Java Exception Classes

Java Exception Keywords
Keyword Description
try
The ”try” keyword is used to specify a block where we
should place an exception code. It means we can’t use try
block alone. The try block must be followed by either catch
or finally.
catch
The ”catch” block is used to handle the exception. It
must be precededby try block which means we can’t use
catch block alone. It can be followed by finally block later.
finally
The ”finally” block is used to execute the necessary
code of the program. It is executed whether an
exception is handled or not.
throw The ”throw” keyword is used to throw an exception.
throws
The ”throws” keyword is used to declare exceptions.
It specifies that there may occur an exception in the
method. It doesn’t throw an exception. It is always used
with method signature.

Java try-catch Block
Java try block is used to enclose the code that might throw an exception.If an
exception occurs at the particular statement in the try block, the rest of the block
code will not execute. So, it is recommended not to keep the code in try block that
will not throw an exception.
Java catch block is used to handle the Exception by declaring the type of
exception within the parameter. The declared exception must be the parent class
exception ( i.e., Exception) or the generated exception type.

Try-catch Example
Figure 24: Try-catch block example
Figure 25: Output of the above c ode

JAVA Basics Presentation for introduction to JAVA programming languauge

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