Java Intro
Java is a popular, object-oriented programming language used for building platform-independent applications. Java code is compiled into bytecode, which runs on the Java Virtual Machine (JVM), enabling cross-platform compatibility.
Console Output: print
and println
System.out.print()
— prints text without moving to a new line.System.out.println()
— prints text and moves to the next line.
Example:
System.out.print("Hello ");
System.out.println("World!");
Output:
Hello World!
Comments in Java
- Single-line comment: Use
//
// This is a single-line comment
- Multiple-line (block) comment: Use
/* ... */
/* This is a
multi-line comment */
Data Types
Data type | Description | Example |
---|---|---|
int |
Integer numbers | int age = 25; |
char |
Single character | char letter = 'A'; |
double |
Double-precision floating point | double price = 10.99; |
float |
Single-precision floating point | float pi = 3.14f; |
boolean |
True or false values | boolean isJavaFun = true; |
String |
Sequence of characters (not primitive) | String name = "Alice"; |
If-Else Condition
if (condition) {
// code to execute if condition is true
} else {
// code to execute if condition is false
}
Example:
int num = 10;
if (num > 5) {
System.out.println("Greater than 5");
} else {
System.out.println("5 or less");
}
If-Else-If Ladder
if (condition1) {
// code for condition1
} else if (condition2) {
// code for condition2
} else {
// code if none of above conditions are true
}
Operators
Operator | Description |
---|---|
< | Less than |
> | Greater than |
<= | Less than or equal to |
>= | Greater than or equal to |
== | Equal to |
&& | Logical AND |
|| | Logical OR |
! | Logical NOT (negation) |
++ | Increment (increase by 1) |
-- | Decrement (decrease by 1) |
% | Modulus (remainder of division) |
Example:
int a = 5;
int b = 2;
System.out.println(a % b); // Outputs 1
String Comparison
equals()
— checks if two strings are exactly equal (case-sensitive).equalsIgnoreCase()
— checks if two strings are equal, ignoring case.
String s1 = "hello";
String s2 = "Hello";
System.out.println(s1.equals(s2)); // false
System.out.println(s1.equalsIgnoreCase(s2)); // true
Switch Statement
int day = 3;
switch(day) {
case 1:
System.out.println("Monday");
break;
case 2:
System.out.println("Tuesday");
break;
case 3:
System.out.println("Wednesday");
break;
default:
System.out.println("Invalid day");
}
Loops
For Loop
for (int i = 0; i < 5; i++) {
System.out.println(i);
}
While Loop
int i = 0;
while (i < 5) {
System.out.println(i);
i++;
}
Do-While Loop
int i = 0;
do {
System.out.println(i);
i++;
} while (i < 5);
Break and Continue
break
— exits the loop immediately.continue
— skips the current iteration and proceeds to the next.
Example:
for (int i = 0; i < 10; i++) {
if (i == 5)
break; // loop stops when i == 5
if (i % 2 == 0)
continue; // skip even numbers
System.out.println(i); // prints odd numbers less than 5
}