How to Use the Java Compiler

To use the Java Compiler, follow these steps:

  1. In the code editor, write your Java code.
  2. Click the "RUN" button to compile and run your code.
  3. The output will be displayed in the console beside the code editor.

Taking Inputs

In Java, you can take inputs from the user in various ways. Here are some examples:

String Input

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter a string:");
        String input = scanner.nextLine();
        System.out.println("You entered: " + input);
    }
}

Array of Numbers

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter numbers separated by spaces:");
        String[] numbers = scanner.nextLine().split(" ");
        System.out.println("Array of numbers: ");
        for (String number : numbers) {
            System.out.println(number);
        }
    }
}

Matrix Input

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the number of rows:");
        int rows = scanner.nextInt();
        int[][] matrix = new int[rows][];
        for (int i = 0; i < rows; i++) {
            System.out.println("Enter row " + (i + 1) + " separated by spaces:");
            String[] row = scanner.nextLine().split(" ");
            matrix[i] = new int[row.length];
            for (int j = 0; j < row.length; j++) {
                matrix[i][j] = Integer.parseInt(row[j]);
            }
        }
        System.out.println("Matrix: ");
        for (int[] row : matrix) {
            for (int num : row) {
                System.out.print(num + " ");
            }
            System.out.println();
        }
    }
}

Importing Libraries

Java has a rich set of built-in libraries that can be imported and used in your programs. Here are some examples:

Using the Math Library

public class Main {
    public static void main(String[] args) {
        double result = Math.sqrt(25);
        System.out.println("Square root of 25 is " + result);
    }
}

Using the Arrays Library

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] numbers = {5, 2, 8, 7, 1};
        Arrays.sort(numbers);
        System.out.println(Arrays.toString(numbers));
    }
}

Using the ArrayList Class

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Cherry");
        System.out.println(list);
    }
}

Syntax 101

Java is a statically-typed, object-oriented programming language. Here's a primer on the major syntax basics of Java:

Variables

Variables in Java must be declared before they can be used. You must also specify the type of data the variable can hold.

int age = 25; // Integer
double pi = 3.14; // Double
boolean isAdult = true; // Boolean
char

initial = 'J'; // Character
String name = "John Doe"; // String

Arrays

Arrays in Java are used to store multiple values in a single variable.

int[] numbers = {1, 2, 3, 4, 5}; // Array of integers

Control Structures

Java includes control structures such as if, else, for, while, and switch.

// If-Else
if (age > 18) {
    System.out.println("Adult");
} else {
    System.out.println("Minor");
}

// 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++;
}

// Switch
switch (day) {
    case "Monday":
        System.out.println("Start of the work week");
        break;
    case "Friday":
        System.out.println("End of the work week");
        break;
    default:
        System.out.println("Midweek");
}

Functions

Functions in Java are declared within a class. They are defined with the void keyword if they do not return a value.

void greet() {
    System.out.println("Hello, world!");
}

greet(); // Calls the function

Object-Oriented Programming (OOP)

Java is an object-oriented programming language. This means that it focuses on objects and classes.

class Car {
    String brand; // Field
    int year; // Field

    Car(String brand, int year) { // Constructor
        this.brand = brand;
        this.year = year;
    }

    void start() { // Method
        System.out.println("Car is starting.");
    }
}

Car myCar = new Car("Toyota", 2005); // Create an object of the Car class
myCar.start(); // Call the start method

Java Online Test

A Java online test is an effective way to assess an individual's Java programming skills. These tests typically include a mix of theoretical questions and practical coding challenges. By attempting these tests, candidates can demonstrate their understanding of Java concepts, their problem-solving abilities, and their proficiency in writing efficient code. Java online tests are commonly used in technical interviews, coding bootcamps, and online learning platforms to gauge a learner's understanding and proficiency in Java.