Java for Programmers

                                
// This is an inline comment. It only includes this line.
/*
 This is a block comment. Anything between the asterisks is part of the comment.
*/

                              

                                
System.out.print("I'm first!");
System.out.println("I'm second!");
System.out.print("I'm last!");
/* Prints:
I'm first!I'm second!
I'm last!
*/

                              

                                
// int - stores whole numbers:
int num = 10;
// double - stores decimal numbers:
double dec = 4.99;
// boolean - stores true or false values:
boolean isTrue = true;
// char - stores a single character value:
char firstLetter = 'A';
// String - stores multiple characters:
String message = "hello there";

                              

                                

  public class NumberManipulation {
    public static void main(String[] args) {
        int a = 3; 
        int b = 5;

        // Basic arithmetic operations
        System.out.println("Addition: " + (a + b));        // 8
        System.out.println("Subtraction: " + (a - b));     // -2
        System.out.println("Multiplication: " + (a * b));  // 15
        System.out.println("Division: " + (b / a));         // 1
        System.out.println("Modulus: " + (b % a));          // 2

        // Compound assignment
        int num = 10; 
        num += a; // num = num + a
        System.out.println("After += : " + num);           // 13

        num *= 2; // num = num * 2
        System.out.println("After *= : " + num);           // 26
    }
}



                              

                                
boolean expression1 = false;
boolean expression2 = false;
boolean expression3 = true;
if (expression1) {
  System.out.println("The first expression is true");
} else if (expression2) {
  System.out.println("The second expression is true");
} else if (expression3) {
  System.out.println("The third expression is true");
} else {
  System.out.println("All other expressions were false");
}
// Prints: The third expression is true

                              

                                
// Comparison Operators:
int a = 1;
int b = 5;
System.out.println(a > b); // Prints: false
System.out.println(a < b); // Prints: true
System.out.println(a >= 1); // Prints: true
System.out.println(a + 4 <= b); // Prints: true
System.out.println(a == 1); // Prints: true
System.out.println(b != 5); // Prints: false
// Logical Operators:
System.out.println(!true); // Prints: false
System.out.println(!false); // Prints: true
System.out.println(true && true); // Prints: true
System.out.println(true && false); // Prints: false
System.out.println(false && true); // Prints: false
System.out.println(false && false); // Prints: false
System.out.println(true || true); // Prints: true
System.out.println(true || false); // Prints: true
System.out.println(false || true); // Prints: true
System.out.println(false || false); // Prints: false

                              

                                
// An example of a while loop:
int x = 0;
while (x < 2) {
  System.out.println(x);
  x++;
} // Prints: 0 and 1
// An example of a do-while loop:
do {
  System.out.println("Impossible!");
} while (2 == 4); // Prints: Impossible!
  // An example of a for loop:
for (int i = 0; i < 10; i++) {
 System.out.println(i);
} // Prints: 0 to 9, inclusive
// An example of a for-each loop:
String[] colors = {"Red", "Blue", "Yellow"};
for (String c : colors) {
 System.out.println(c);
} // Prints: Red, Blue, and Yellow

                              

                                
// An example of a break statement:
for (int i = 0; i < 10; i++) {
  System.out.println(i);
  if (i == 4) {
    break;
  }
} // Prints: 0 to 4, inclusive
// An example of a continue statement:
int[] numbers = {1, 2, 3, 4, 5};
for (int i = 0; i < numbers.length; i++) {
  if (numbers[i] % 2 == 0) {
    continue;
  }
  System.out.println(numbers[i]);
} // Prints 1, 3, and 5

                              

                                
/*
The following method is a public method called findSum. The method takes in two int parameters called int1 and int2. This method returns an int value.
*/
public static int findSum(int num1, int num2) {
  return num1 + num2;
}
public static void main(String[] args) {
  // Call the method with the arguments 3 and 4
  int sum = findSum(3,4);
  System.out.println(sum); // Prints: 7
}

                              

                                
// Using the .length() method:
String str = "Hello World!";
System.out.println(str.length()); // Prints: 12
// Using the .concat() method:
String name = "Hello";
name = name.concat("World");
System.out.println(name); // Prints: HelloWorld
// Using the .equals() method:
String flavor1 = "Mango";
String flavor2 = "Matcha";
System.out.println(flavor1.equals(flavor2)); // Prints: false 
// Using the .indexOf() method:
String letters = "ABCDEFGHIJKLMN";
System.out.println(letters.indexOf("C")); // Prints: 2
// Using the .charAt() method:
String currency = "Yen";
System.out.println(currency.charAt(2)); // Prints: n
// Using the .substring() method
String line = "It was the best of times, it was the worst of times.";
System.out.println(line.substring(26)); // Prints: it was the worst of times.
System.out.println(line.substring(7, 24)); // Prints: the best of times

                              

                                
String[] animals = {"Giraffe", "Elephant", "Toucan"};
// Access an element via its index:
System.out.println(animals[0]); // Prints: Giraffe
// Change an element value:
animals[1] = "Lion";
// Find number of elements in an array:
System.out.println(animals.length); // Prints: 3
// Traverse array using for loop:
for (int i = 0; i < animals.length; i++) {
  System.out.println(animals[i]);
}
/* Prints:
Giraffe
Lion
Toucan
*/
// Traverse array using enhanced for loop:
for (String animal : animals) {
  System.out.println(animal);
}
/* Prints:
Giraffe
Lion
Toucan
*/

                              

                                
int[][] matrix = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
// Access element at row 2, column 3:
System.out.println(matrix[1][2]); // Prints: 6
// Traverse multidimensional array:
for (int i = 0; i < matrix.length; i++) {
  for (int j = 0; j < matrix[i].length; j++) {
    System.out.print(matrix[i][j] + " ");
  }
  System.out.println();
}
/* Prints:
1 2 3 
4 5 6 
7 8 9 
*/

                              

                                
import java.util.ArrayList;

ArrayList<string> list = new ArrayList<>();
list.add("First");
list.add("Second");
list.add("Third");
// Access an element via its index:
System.out.println(list.get(1)); // Prints: Second
// Remove an element:
list.remove(2);
// Find number of elements in ArrayList:
System.out.println(list.size()); // Prints: 2
// Traverse ArrayList:
for (String item : list) {
  System.out.println(item);
}
/* Prints:
First
Second
*/

                              

                                
public class Car {
  String color;
  String model;
  int year;

  // Method to display car details
  public void displayDetails() {
    System.out.println("Model: " + model);
    System.out.println("Color: " + color);
    System.out.println("Year: " + year);
  }
}
// Create an instance of Car and use it:
Car myCar = new Car();
myCar.color = "Red";
myCar.model = "Toyota";
myCar.year = 2020;
myCar.displayDetails();
/* Prints:
Model: Toyota
Color: Red
Year: 2020
*/

                              

                                
public class Animal {
  String name;
  public void makeSound() {
    System.out.println("Animal sound");
  }
}
public class Dog extends Animal {
  public void bark() {
    System.out.println("Woof!");
  }
}
// Use inheritance:
Dog myDog = new Dog();
myDog.name = "Buddy";
myDog.makeSound(); // From Animal class
myDog.bark(); // From Dog class
/* Prints:
Animal sound
Woof!
*/

                              

                                
class Bird {
  public void fly() {
    System.out.println("Bird flies");
  }
}
class Penguin extends Bird {
  @Override
  public void fly() {
    System.out.println("Penguins can't fly");
  }
}
// Use polymorphism:
Bird myBird = new Bird();
Bird myPenguin = new Penguin();
myBird.fly(); // Prints: Bird flies
myPenguin.fly(); // Prints: Penguins can't fly

                              

                                
public class Person {
  private String name;
  private int age;

  // Getter and setter for name
  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  // Getter and setter for age
  public int getAge() {
    return age;
  }

  public void setAge(int age) {
    this.age = age;
  }
}
// Use encapsulation:
Person p = new Person();
p.setName("John");
p.setAge(30);
System.out.println(p.getName()); // Prints: John
System.out.println(p.getAge()); // Prints: 30

                              

                                
import java.util.HashMap;

HashMap<string, integer=""> map = new HashMap<>();
map.put("One", 1);
map.put("Two", 2);
map.put("Three", 3);
// Retrieve a value:
System.out.println(map.get("Two")); // Prints: 2
// Remove a key-value pair:
map.remove("Three");
// Iterate over HashMap:
for (String key : map.keySet()) {
  System.out.println(key + " : " + map.get(key));
}
/* Prints:
One : 1
Two : 2
*/

                              

                                
import java.util.HashSet;

HashSet<string> set = new HashSet<>();
set.add("Apple");
set.add("Banana");
set.add("Apple");
// Print HashSet:
for (String fruit : set) {
  System.out.println(fruit);
}
/* Prints:
Apple
Banana
*/

                              

                                
import java.util.LinkedList;

LinkedList<string> list = new LinkedList<>();
list.add("First");
list.add("Second");
list.addLast("Third");
// Retrieve an element:
System.out.println(list.get(1)); // Prints: Second
// Remove an element:
list.removeFirst();
// Iterate over LinkedList:
for (String item : list) {
  System.out.println(item);
}
/* Prints:
Second
Third
*/