OOP’s Using JAVA Module 2

Topics Covered
Data Types
Operators
Control Statements
Variables & Arrays
String Handling
The String Constructors
String Length
Special String Operations
Character Extraction
String Comparison
Modifying a String
String Buffer

Data Types
Data types specify the different sizes and values that can be stored in the variable. There are two types of data types in Java
Primitive data types: The primitive data types include Boolean, char, byte, short, int, long, float and double.
Non-primitive data types: The non-primitive data types include Classes, Interfaces, and Arrays,Strings.
In Java language, primitive data types are the building blocks of data manipulation. These are the most basic data types available in Java language.

Operators in Java
Operator in Java is a symbol that is used to perform operations.
Java divides the operators into the following groups:
Arithmetic operators
Assignment operators
Comparison operators
Logical operators
Conditional operators

Arithmetic Operator
Arithmetic operators are used to perform common mathematical operations.

Comparison operators
comparison operators are used to compare two values

Assignment operators
Assignment operators are used to assign values to variables
For example, we use the assignment operator (=) to assign the value to variable x:
in x=10

Logical operators
Logical operators are used to determine the logic between variables or values

Conditional operators
Consider this example
Int a=30;
Int b=40;
In x=(a>b)?a:b;

Control Statements
There are three types of control flow statements.
Conditional statements: based on particular condition the selected block will be executed
if
if –else
else-if
Switch
2. Loop statements: The same code will be Repeated multiple times
for
while
do-while
3. Transfer statements: The control is transfer from one location to another location is called transfer statements
break
continue

Control Statement Conditional statements
If Statement
To take only one option
Syntax of if statement is given below.
if(condition) {
True body; //executes when condition is true
}

Example of “if” statement
Program 1
class Student {
public static void main(String[] args) {
int x = 20;
int y = 10;
if(x>y) { //if Condition
System.out.println("x is greater than y");
}
}
}

Control Statement
Decision-Making statements
“if-else” statement
Two option available.
The if-else statement is an extension to the if-statement, which uses another block of code, i.e., else block.
The else block is executed if the condition of the if-block is evaluated as false.
Syntax:
if(condition) {
True body; //executes when condition is true
}
else{
False body; //executes when condition is false
}

Example of “if else” statement
Program 2
class Student {
public static void main(String[] args) {
int x = 20;
if(x> 18) {
System.out.println(“Eligible for marriage….");
} else {
System.out.println(“Not eligible for marriage try after some time….");
}
}
}

Control Statement
Decision-Making statements
“if-else-if” statement
The if-else-if statement contains the if-statement followed by multiple else-if statements.
In other words, we can say that it is the chain of if-else statements that create a decision tree where the program may enter in the block of code where the condition is true.
Syntax
if(condition 1) {
statement 1; //executes when condition 1 is true
}
else if(condition 2) {
statement 2; //executes when condition 2 is true
}
else {
statement 2; //executes when all the conditions are false
}

Example of “if else if” statement
Program 3
class Positive {
public static void main(String[] args) {
int number=-13;
if(number>0){
System.out.println("POSITIVE");
}else if(number<0){
System.out.println("NEGATIVE");
}else{
System.out.println("ZERO");
}
}
}

Example of “if else if” statement
Program 3
class Sleep {
public static void main(String[] args) {
int a=10;
if(a==10){
System.out.println(“Aslam don’t sleep");
}
else if(a==20){
System.out.println(" Amar don’t sleep ");
}
else if(a==30){
System.out.println(“Umar don’t sleep");
}
else{
System.out.println(" Bharath don’t sleep ");
}
}
}

Control Statement
Decision-Making statements
switch statement
The Java switch statement executes one statement from multiple conditions. It is like if-else-if ladder statement. The switch statement works with byte, short, int.
Points to be noted about switch statement:
The case variables can be int, short, byte, char. String type is also supported since version 7 of Java
Cases cannot be duplicate
Default statement is executed when any of the case doesn't match the value of expression. It is optional.

The syntax to use the switch
switch(argument){
case value1: Statements;
break; //optional
case value2: Statements;
break; //optional
......
default:
code to be executed if all cases are not matched;
}

Example of “Switch” statement
Program 5
EX:
class SwitchExample {
public static void main(String[] args) {
//Declaring a variable for switch expression
int a=20;
//Switch expression
switch(a){
//Case statements
case 10: System.out.println("10");
break;
case 20: System.out.println("20");
break;
case 30: System.out.println("30");
break;
//Default case statement
default:System.out.println("Not in 10, 20 or 30");
}
}
}
EX:
class SwitchExample2 {
public static void main(String[] args) {
int a=20;
//switch expression with int value
switch(a){
//switch cases without break statements
case 10: System.out.println("10");
case 20: System.out.println("20");
case 30: System.out.println("30");
default:System.out.println("Not in 10, 20 or 30");
}
}
}

Loop Statements
Loop statements: The same code will be Repeated multiple times
for while
do-while

Loop Statements
for
In Java, for loop is similar to C and C++
It enables us to initialize the loop variable, check the condition, and increment/decrement in a single line of code.
We use the for loop only when we exactly know the number of times, we want to execute the block of code.
Syntax
for(initialization, condition, increment/decrement) {
//block of statements
}

Example of “for loop”
Program 5
class Test {
public static void main(String[] args) {
for(int i= 0; i<=10; i++) {
System.out.println(“Good Morning…." );
}
}
}

Loop Statements
While
The while loop is also used to iterate over the number of statements multiple times.
For loop is recommended when we have :(start;end_cond;incre_decre)
while loop is recommended when we have the only condition check.
syntax :
while(condition){
body
}
The body will be executed until the condition is fail

Example of “while”
Program 6
class Test {
public static void main(String[] args) {
// for loop to printing the data 10 times
for(int j=0;j<10;j++)
{
System.out.println(“Good Morning..”);
}
// while loop to printing the data 10 times
Int i=0;
while(i<10) {
System.out.println(“Good Evening..”);
i++;
}
}
}
//To print the data 10-time it is recommended to use for loop.

Loop Statements
do While
If you want execute the body first without condition check then use do while.
The syntax
do
{
//body
} while (condition);

Loop Statements
do While
Ex:
class Test {
public static void main(String[] args) {
do {
System.out.println(“Good Morning”);
}while(20<10);
}
}
EX:
class Test {
public static void main(String[] args) {
Int i=0;
do {
System.out.println(“Good Morning”);
i++;
}while(i<10);
}
}

Jump Statement
Jump statements are used to transfer the control of the program to the specific statements.
There are two types of jump statements in Java, i.e., break and continue.
break statement- As the name suggests, the break statement is used to break the current flow of the program and transfer the control to the next statement outside a loop or switch statement
continue statement –The continue statement break one iteration(in the loop),if a specified condition occurs and continues next iteration in the loop.

Jump Statement

Variables in JAVA
A variables are used to store the values by using that value we are achieving the project requirements.
A variable is assigned with a data type.
There are three types of variables in java:
local
instance
static

Variables in JAVA
1) Local Variable
A variable declared inside the method is called local variable.
You can use this variable only within that method
other methods in the class aren't even aware that the variable exists.
Void m1()
{
Int a=10; // Local variables
System.out.println(a); //Possible
}
Void m2()
{
System.out.println(a); //Not Possible
}

2) Instance Variable
A variable declared inside the class but outside the method.
Accessing done through object .
Direct access.
EX:
class variable
{
int a=10;//instance variable
public static void main(String args[])
{
variable obj=new variable(); /* object creation*/
System.out.println(obj.a); ------//10
}
}

3) Static variable
A variable that is declared as static is called a static variable.
Memory allocation for static variables happens only once.
Direct access.
EX:
class variable
{
static int a=10;//static variable
public static void main(String args[])
{
System.out.println(a); ------//10
}
}

Example of “Variables”
Program 9
EX:
class variable
{
int a=10;//instance variable
static int b=10;//static variable
public static void main(String args[])
{
int c=10;//Local variable System.out.println(b);
System.out.println(c);
variable obj=new variable(); /* object creation*/
System.out.println(obj.a); ------//10
}
}

ARRAY in JAVA
Arrays are used to store the group of elements and these elements are homogenous & fixed number
int[] a={10,20,30,40};
double [] d={10.2,20.6,2.5};
Arrays are indexed based, index start from zero.

EX:
class Test
{
int[] a={10,20,30,40};
public static void main(String args[])
{
System.out.println(a[0]);
System.out.println(b[1]);
System.out.println(c[2]);
System.out.println(d[3]);
for(int i=0;i
{
System.out.println(a[i]);
}
}
}

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.
There are two types of array.
Single Dimensional Array
Multidimensional Array

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.
There are two ways to create String object:
By string literal (String s="welcome"; )
By new keyword (String s=new String("Welcome");

Example of “String”
Program 10
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);
}}

String Handling
The Java String class length() method finds the length of a string. The length of the Java string is the same as the Unicode code units of the string.
Syntax
public int length()
public class LengthExample{
public static void main(String args[]){
String s1="javatpoint";
String s2="python";
System.out.println("string length is: "+s1.length());//10 is the length of javatpoint string
System.out.println("string length is: "+s2.length());//6 is the length of python string
}}
Example of “String Length”
Program 11

Special String Operations
There are 4 types of special string Operations
String Literals
String Concatenation
String Concatenation with Other Data Types
String Conversion and toString( )
String literal is created by using double quotes.
For Example:
String s="javaguides";
String Concatenation can be done using + operator, which concatenates two strings, producing a String object.
For Example:
String age = "9";
String s = "He is " + age + " years old.";
System.out.println(s);

You can concatenate strings with other types of data.
For example
int age = 9;
String s = "He is " + age + " years old.";
System.out.println(s);
String Conversion and toString( ) : valueOf() method
For Example
valueOf( )(The valueOf( ) method converts data from its internal format into a human-readable form.)
public static String valueOf(boolean b)
public static String valueOf(char c)
public static String valueOf(char[] c)
public static String valueOf(int i)
public static String valueOf(long l)

String Handling
Character Extraction
String is treated as an object in Java so we can’t directly access the characters that comprise a string.
There are several ways by which characters can be extracted from String class object.
charAt() -- method is used to extract a single character at an index.
char charAt(int index)
getChars() -- used to extract more than one character.
void getChars(int stringStart, int stringEnd, char arr[], int arrStart)
getBytes() -- extract characters from String object and then convert the characters in a byte array.
byte [] getBytes()
toCharArray() -- alternative of getChars() method.
char [] toCharArray()

Example of “Character Extraction”
Program 11
class temp
{
public static void main(String...s)
{
String str="Hello";
char ch=str.charAt(2);
System.out.println(ch);
}
}
class temp
{
public static void main(String...s)
{
String str="Hello World";
char ch[]=new char[4];
str.getChars(1,5,ch,0);
System.out.println(ch);
}
}
class temp
{
public static void main(String...s)
{
String str="Hello World";
char ch[]=str.toCharArray();
System.out.println(ch);
}
}

String Comparison
We can compare String in Java on the basis of content a
It is used in
authentication (by equals() method),
sorting (by compareTo() method),
reference matching (by == operator).
There are three ways to compare String in Java:
By Using equals() Method
By Using == Operator
By compareTo() Method

Example of “String Comparision”
Program 12
class Teststringcomparison1{
public static void main(String args[]){
String s1="Sachin";
String s2="Sachin";
String s3=new String("Sachin");
String s4="Saurav";
System.out.println(s1.equals(s2));//true
System.out.println(s1.equals(s3));//true
System.out.println(s1.equals(s4));//false
}
}
class Teststringcomparison3{
public static void main(String args[]){
String s1="Sachin";
String s2="Sachin";
String s3=new String("Sachin");
System.out.println(s1==s2);//true (because both refer to same instance)
System.out.println(s1==s3);//false(because s3 refers to instance created in nonpool)
}
}
class Teststringcomparison4{
public static void main(String args[]){
String s1="Sachin";
String s2="Sachin";
String s3="Ratan";
System.out.println(s1.compareTo(s2));//0
System.out.println(s1.compareTo(s3));//1(because s1>s3)
System.out.println(s3.compareTo(s1));//-1(because s3 < s1 )
}
}

Modifying a String
Methods for modifying a String objects.
substring()
susubstring(int beginIndex)
bstring(int beginIndex, int endIndex)
concat() -- We can concatenate two strings using concat( )
replace()
String replace(char original, char replacement)
String replace(CharSequence original, CharSequence replacement)
replaceAll() – Replaces each substring of this string that matches the given regular expression with the given replacement.
replaceAll(String regex, String replacement)
replaceFirst() -- Replaces the first substring of this string that matches the given regular expression with the given replacement.
replaceFirst(String regex, String replacement)
trim() -- The trim( ) method returns a copy of the invoking string from which any leading and trailing whitespace has been removed.
String trim( )

StringBuffer
A string buffer is like a String, but can be modified
append()
insert()
replace()
delete()
reverse()
capacity()

Example of “String Buffer”
Program 13
StringBuffer Class append() Method
class StringBufferExample1{
public static void main(String args[]){
StringBuffer sb=new StringBuffer("Hello ");
sb.append("Java");
System.out.println(sb);
} }

StringBuffer insert() Method
class StringBufferExample2{
public static void main(String args[]){
StringBuffer sb=new StringBuffer("Hello ");
sb.insert(1,"Java");//now original string is changed
System.out.println(sb);//prints HJavaello
}
}

StringBuffer replace() Method
class StringBufferExample3{
public static void main(String args[]){
StringBuffer sb=new StringBuffer("Hello");
sb.replace(1,3,"Java");
System.out.println(sb);//prints HJavalo
}
}

StringBuffer delete() Method
class StringBufferExample4{
public static void main(String args[]){
StringBuffer sb=new StringBuffer("Hello");
sb.delete(1,3);
System.out.println(sb);//prints Hlo
}
}

StringBuffer capacity() Method
class StringBufferExample5{
public static void main(String args[]){
StringBuffer sb=new StringBuffer();
System.out.println(sb.capacity());//default 16
sb.append("Hello");
System.out.println(sb.capacity());//now 16
sb.append("java is my favourite language");
System.out.println(sb.capacity());//now (16*2)+2=34 i.e (oldcapacity*2)+2
}
}

StringBuffer reverse() Method
class StringBufferExample6{
public static void main(String args[]){
StringBuffer sb=new StringBuffer("Hello");
sb.reverse();
System.out.println(sb);//prints olleH
}
}