Download a compiler in Java:
Open google and download Java compiler for windows.
After we can see in downloads folder.
Now right click and open jdk folder and install it.
After open My computer and open c drive we can see program files folder and open we can see in that java has been installed.
Open jdk we can see bin folder.
How to set path in java:
Right click on MyComputer - properties.
Click on ok.
Setting path is completed.
Open start menu and enter command prompt (or) windows + R button run opens enter cmd.
Command prompt opened we can check whether java is running or not.
Why java:
We write the program in English language which we can understand but JVM cant understand.
Java compiler will convert our English language program to byte which JVM can understand.
Once we compile our java program it will generate .class file with class name which has byte code.
Why we write a program:
To execute it right for that we have to use Java ClassName
javac for compiling the program.
HelloWorld program:
Data Types:
Variable initiation:
Used to declare a variable.
Variable is a piece of memory that contains data.
We can see the error that variable is not initialised.
Syntax for variable initiation:
Eg:
int number = 10;
Different variables:
Local variables:
Declared inside a method, can be accessible within the same method.
Class variables:
Static variables declared inside a class.
Instance variables:
Non-static variables declared inside a class.
Eg:
class A {
int data = 50; //instance variable
static int m = 100; //static variable
void method() {
int n = 90; //local variable
}
}
Loops:
Particular block which will execute a set of statements till the block is true.
Different kinds:
For:
Executes for certain number of iterations.
Syntax:
for(initialization; condition; increment / decrement)
{
statements
}
Eg:
While:
Executes till the condition false, there is no fixed number of iterations.
Syntax:
while(condition)
{
statements
increment / decrement
}
Executes at least once, then it will check for the condition.
Syntax:
do {
statements
increment / decrement
}(condition);
If statement:
Syntax:
if(condition) {
//code to be executed
}
Eg:
Syntax:
if(condition) {
//code if condition is true
}
else {
//code if condition is false
}
Eg:
Syntax:
if(condition1) {
//code if it is true
}
else if(condition2) {
//code executes if it is true
}
else if(condition3) {
//code executes if it is true
}
...
else {
//code executes if it is false
}
Eg:
Switch:
Syntax:
switch(expression) {
case value1:
//code;
break;
case value2:
//code;
break;
....
default:
code executes if all cases are not matched;
}
Break:
Syntax:
jump-statement;
break;
Syntax:
jump-statement;
continue;
Add two strings:
String concatenation forms a new string that is combination of multiple strings.
2 ways:
String concatenation (+) operator.
Concat() method.
Partial string:
A part of string is called substring.
Index starts from 0.
Start index is inclusive and end index is exclusive.
Eg: hello
string s="hello";
System.out.println(s.substring(0,2));
output: he
0 points to h and 2 points to l but end index is exclusive.
Eg:
Find starting point for a string:
Read from user input and write to user output syntax:
Count the number of occurences of a substring in a string:
Read from a file and write to a file:
Reading a file:
Create a sample text in notepad and save it with .txt extension.
Enter some text in it and save it.
While writing in a program we have to specify the particular path where we have stored it.
Now, in output we can see the entered text it reads from a file.
While writing a program set the path and enter a filename with .txt extension.
After compiling and executing the program we can see the success message and file will be created in our specified location.
We can see in E drive because i specified the location as E drive in my program so .txt will be created.
Now, open the example1.txt file we can see the message which is file writer.
Draw a Line:
Draw a Circle:
Draw a Rectangle:
First non repeated character in a given string:
Program to sum a number in given string:
Database connection:
To connect to a database we have to install mysql installer.
But still we are getting error.
We can see connection successfull to database.
