#Java basic
Topic
Index
1.Introduction of java
2.Operators & Variables
3.Data Types
4.Loops
5.Conditions
6.Statements
7.Function
8.String
9.Array
10.File Handing
11.Exception
12.Recurion
Introduction in java
Java is class-based Object-Oriented Programming language and
is designed to have as few Impelimention Dependencies as Possible
About of Java JDK, JRE and JVM
JVM (Java Virtual Machine) is an abstract
machine that enables your computer to run a Java program.
What is JRE
JRE (Java Runtime Environment) is a software package that provides
Java class libraries, Java Virtual Machine (JVM),
and other components that are required to run Java applications.
What is JDK
JDK (Java Development Kit) is a software development kit required to develop
applications in Java. When you download JDK, JRE is also downloaded with it.
In addition to JRE, JDK also contains a number of development tools
(compilers, JavaDoc, Java Debugger, etc).
*Simple Program in java*
class Hello{
public static void main(String[] args){
System.out.println("Hello Java");
}
}
Java Basic Input and Output
##java Output
System.out.println(); or
System.out.print(); or
System.out.printf();
Difference between println(), print() and printf()
print() - It prints string inside the quotes.
println() - It prints string inside the quotes similar like print() method. Then the cursor moves to the beginning of the next line.
printf() - It provides string formatting (similar to printf in C/C++ programming).
class Print {
public static void main(String[] args) {
System.out.println("1. println ");
System.out.println("2. println ");
System.out.print("1. print ");
System.out.print("2. print");
}
}Printing Variables and Literals
##Print Variables
class Variables {
public static void main(String[] args) {
Double number = -10.6;
System.out.println(5);
System.out.println(number);
}
}JAVA INPUT
Java provides different ways to get input from the user. However, in this tutorial, you will learn to get input from user using the object of Scanner class.
In order to use the object of Scanner, we need to import java.util.Scanner package.
import java.util.Scanner;
Then, we need to create an object of the Scanner class. We can use the object to take input from the user.
// create an object of Scanner
Scanner input = new Scanner(System.in);
// take input from the user
int number = input.nextInt();##Get Integer Input From the User
import java.util.Scanner;
class Input {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter an integer: ");
int number = input.nextInt();
System.out.println("You entered " + number);
// closing the scanner object
input.close();
}
}
##Get float, double and String Input
import java.util.Scanner;
class Input {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
// Getting float input
System.out.print("Enter float: ");
float myFloat = input.nextFloat();
System.out.println("Float entered = " + myFloat);
// Getting double input
System.out.print("Enter double: ");
double myDouble = input.nextDouble();
System.out.println("Double entered = " + myDouble);
// Getting String input
System.out.print("Enter text: ");
String myString = input.next();
System.out.println("Text entered = " + myString);
}
}In computer programming, comments are a portion of the program that are completely ignored by Java compilers. They are mainly used to help programmers to understand the code.
Types of Comments in Java
In Java, there are two types of comments:
single-line comment
multi-line comment
Single-line Comment
A single-line comment starts and ends in the same line. To write a single-line comment, we can use the // symbol.
// "Hello, World!" program example
class Main {
public static void main(String[] args) {
// prints "Hello, World!"
System.out.println("Hello, World!");
}
}Multi-line Comment
When we want to write comments in multiple lines, we can use the multi-line comment. To write multi-line comments, we can use the /..../ symbol.
/* This is an example of multi-line comment.
* The program prints "Hello, World!" to the standard output.
*/
class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}Variable in java
A variable is a location in memory (storage area) to hold data.
int speedLimit = 80;Here, speedLimit is a variable of int data type and we have assigned value 80 to it.
Print Variable
int Name = "Tej";
System.out.println(Name);Data type in java
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.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 type
int num = 5; // store all integer number
float f = 5.99f; // Store all Float number
String str = "Hello"; //Store String & Sentance
char ch = 'A'; // store a character
boolean bool = true; // Return True or false
System.out.println(num);
System.out.println(f);
System.out.println(str);
System.out.println(bool);
System.out.println(ch);Java Operators Operators are symbols that perform operations on variables and values. Operators in Java can be classified into 5 types:
1.Arithmetic Operators 2.Assignment Operators 3.Relational Operators 4.Logical Operators 5.Unary Operators 6.Bitwise Operators
| Operators | Operation |
|---|---|
| + | Addition |
| - | Subtraction |
| * | Multiplication |
| / | Division |
| % | Modulo Operation |
Arithmetic Operators
class Main {
public static void main(String[] args) {
// declare variables
int a = 12, b = 5;
// addition operator
System.out.println("a + b = " + (a + b));
// subtraction operator
System.out.println("a - b = " + (a - b));
// multiplication operator
System.out.println("a * b = " + (a * b));
// division operator
System.out.println("a / b = " + (a / b));
// modulo operator
System.out.println("a % b = " + (a % b));
}
}2. Java Assignment Operators
| Operators | Example | Operation |
|---|---|---|
| = | a = b; | a = b; |
| += | a += b; | a = a + b; |
| -= | a -= b; | a = a - b; |
| *= | a *= b; | a = a * b; |
| /= | a /= b; | a = a / b; |
| %= | a %= b; | a = a % b; |
class Main {
public static void main(String[] args) {
// create variables
int a = 4;
int var;
// assign value using =
var = a;
System.out.println("var using =: " + var);
// assign value using =+
var += a;
System.out.println("var using +=: " + var);
// assign value using =*
var *= a;
System.out.println("var using *=: " + var);
}
}3. Java Relational Operators Relational operators are used to check the relationship between two operands.
| Operators | Example | Operation |
|---|---|---|
| == | Equal to | a == b; |
| != | Not Equal to | a != b; |
| > | Greater then | a > b; |
| < | Lesst= Then | a < b; |
| <= | GreaterThenequalto | a <= b; |
| >= | LessThenequalto | a >=b; |
class Main {
public static void main(String[] args) {
int a = 7, b = 11;
System.out.println("a is " + a + " and b is " + b);
System.out.println(a == b); // false
System.out.println(a != b); // true
System.out.println(a > b); // false
System.out.println(a < b); // true
System.out.println(a >= b); // false
System.out.println(a <= b); // true
}
}4. Java Logical Operators Logical operators are used to check whether an expression is true or false. They are used in decision making.
| Operators | Example | Operation |
|---|---|---|
| && (Logical AND) | expression1 && expression2 | true only if both are true |
| (Logical OR) | expression1 OR expression2 | true if either expression1 or expression2 is true |
| ! (Logical NOT) | !expression | true if expression is false and vice versa |
class Main {
public static void main(String[] args) {
System.out.println((5 > 3) && (8 > 5)); // true
System.out.println((5 > 3) && (8 < 5)); // false
System.out.println((5 < 3) || (8 > 5)); // true
System.out.println((5 > 3) || (8 < 5)); // true
System.out.println((5 < 3) || (8 < 5)); // false
System.out.println(!(5 == 3)); // true
System.out.println(!(5 > 3)); // false
}
}- Java if (if-then) Statement
The syntax of an if-then statement is:
if (condition) {
// statements
}if condition evaluates to true, statements are executed
if condition evaluates to false, statements are skipped
2. Java if...else (if-then-else) Statement
The if Statement execute When condition is true Otherwise Else part is execute
Syntax of if-else statement
if (condition) {
// codes in if block
}
else {
// codes in else block
}
3. Java if...else...if Statement
In Java, we have an if...else...if ladder, that can be used to execute one block of code among multiple other blocks.
if (condition1) {
// codes
}
else if(condition2) {
// codes
}
else if (condition3) {
// codes
}
.
.
else {
// codes
}
4.Java Nested if..else Statement
In Java, it is also possible to use if..else statements inside an if...else statement. It's called the nested if...else statement.
Here's a program to find the largest of 3 numbers using the nested if...else statement.
class Main {
public static void main(String[] args) {
// declaring double type variables
Double n1 = -1.0, n2 = 4.5, n3 = -5.3, largest;
// checks if n1 is greater than or equal to n2
if (n1 >= n2) {
// if...else statement inside the if block
// checks if n1 is greater than or equal to n3
if (n1 >= n3) {
largest = n1;
}
else {
largest = n3;
}
} else {
// if..else statement inside else block
// checks if n2 is greater than or equal to n3
if (n2 >= n3) {
largest = n2;
}
else {
largest = n3;
}
}
System.out.println("Largest Number: " + largest);
}
}The switch statement allows us to execute a block of code among many alternatives.
The syntax of the switch statement in Java is:
switch (expression) {
case value1:
// code
break;
case value2:
// code
break;
...
...
default:
// default statements
}Example: java Switch statement
// Java Program to check the size
// using the switch...case statement
class Main {
public static void main(String[] args) {
int number = 44;
String size;
// switch statement to check size
switch (number) {
case 29:
size = "Small";
break;
case 42:
size = "Medium";
break;
// match the value of week
case 44:
size = "Large";
break;
case 48:
size = "Extra Large";
break;
default:
size = "Unknown";
break;
}
System.out.println("Size: " + size);
}
}FlowChart of Switch statement
In computer programming, loops are used to repeat a block of code.
In Java, there are three types of loops.
1.for loop
2.while loop
3.do...while loop
for loop in java
Java for loop is used to run a block of code for a certain number of times. The syntax of for loop is:
for (initialExpression; testExpression; updateExpression) {
// body of the loop
}Here,
The initialExpression initializes and/or declares variables and executes only once.
The condition is evaluated. If the condition is true, the body of the for loop is executed.
The updateExpression updates the value of initialExpression.
The condition is evaluated again. The process continues until the condition is false.
Flowchart of for loop
In Java, the for-each loop is used to iterate through elements of arrays and collections (like ArrayList). It is also known as the enhanced for loop.
The syntax of the Java for-each loop is:
for(dataType item : array) {
...
}array - an array or a collection
item - each item of array/collection is assigned to this variable
dataType - the data type of the array/collection
java while loop
while (testExpression) {
// body of loop
}
A while loop evaluates the textExpression inside the parenthesis ().
If the textExpression evaluates to true, the code inside the while loop is executed.
The textExpression is evaluated again.
This process continues until the textExpression is false.
When the textExpression evaluates to false, the loop stops.
Flow chart of while loop
Java do...while loop
The do...while loop is similar to while loop. However, the body of do...while loop is executed once before the test expression is checked. For example,
do {
// body of loop
} while(textExpression);
Break Statement
The break statement in Java terminates the loop immediately, and the control of the program moves to the next statement following the loop.
Syntax
break;
Java continue
After the continue statement, the program moves to the end of the loop. And, test expression is evaluated (update statement is evaluated in case of the for loop).
Syntax
continue;
function is a block of code , it takes some input and return some output
--Syntax
returntype functionName(Type arg1 , type arg2)
{
//operation
}
Example
import java.util.*;
//create a class
public class function{
//create a function
public static void printMyName(String name){
System.out.println(name);
return;
}
public static void main(String[] args){
String name = "Tej";
//call function
printMyName(name);
}
}
Array list of item of the same type.
Array is collection of similar datatype.
Syntax
Type[] arrayname = new type[size];
Start indexing at 0 to (n-1)
exple:
int num[] = new int[5]
n=5
n-1 => 5-1;
0 to 4
print an Array
public class printArray{
public static void main(String[] args){
int num[] = new int[3];
num[0] = 1;
num[1] = 2;
num[2] = 3;
for(int i=0; i<=n; i++){
System.out.println(num[i]);
}
}
}
Get input by user in Array
import java.util.*;
public class getInputArray{
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
int size = sc.nextInt();
int number = sc.int[size];
for(int i=0; i<size; i++){
System.out.println(number[i]);
}
}
}
2D-Array in java
Syntax
type[][] arrayname = new type[row][col];
//creation of 2D-Array
int number[][] = new int[3][3];
String is collection of character.
Syntax
String str = "hello my name is TejPrakash Upadhyay";
how to print String
public class printString{
public static void main(String[] args){
String str = "Tej";
String str1 = "Upadhyay";
System.out.println(str);
System.out.println(str1);
}
}
How to get input by user as String
import java.util.*;
public class getInput{
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
String str = sc.nextLine();
System.out.println("Your name is" + str);
}
}
Concatention
String str = "Tej";
String str1 = "Upadhyay";
String full = str +""+str1;
System.out.print("your full Name"+full);
find length any String
varibleName.length()
print one by one Character any String
variavlename.charAt();