Revisiting Java Classes and Object-Oriented Programming

Greetings! Today, we're exploring Java classes, the core building block of Object-Oriented Programming (OOP) in Java. Classes play a pivotal role in structuring code to model real-world entities and behaviors. Through hands-on examples, we'll delve into the fundamental concepts of Java classes, including their structure, methods, and encapsulation. This session aims to enhance your understanding of how classes facilitate better code organization and reusability.

Java Classes Refresher

Let's begin with a refresher on Java classes. Essential to OOP, Java classes bundle relevant data and functions into compact units called objects. Consider a video game character, which is a typical example of a class instance, with specific fields (such as health and strength) and methods (such as attack). Java class GameCharacter {// Fields private String name; private int health; private int strength; // Constructor public GameCharacter(String name, int health, int strength) {this.name = name; this.health = health; this.strength = strength;} // Method public void attack(GameCharacter otherCharacter) {otherCharacter.health -= this.strength;} // Getter methods public String getName() {return name;} public int getHealth() {return health;} public int getStrength() {return strength;}} class Solution {public static void main(String[] args) {// Example usage GameCharacter character1 = new GameCharacter("Hero", 100, 20); GameCharacter character2 = new GameCharacter("Villain", 80, 15); System.out.println(character2.getHealth()); // Prints: 80 character1.attack(character2); // character1 attacks character2 System.out.println(character2.getHealth()); // Prints: 60}} In the code above, the GameCharacter class has fields name, health, and strength . Each of these fields is accessed via getter methods, such as getHealth(), which provide a way to access these private fields from outside the class while maintaining encapsulation. Java classes facilitate the grouping of associated code elements, simplifying their management. Now, let's go through this example step-by-step to better understand how it functions.

Join the 1M+ learners on CodeSignal

Be a part of our community of 1M+ users who develop and demonstrate their skills on CodeSignal

Examples of Java Classes, Methods, and Encapsulation

To further understand Java classes, let's explore another example with a BankAccount class. This example demonstrates modeling real-world entities using object-oriented programming by defining fields like the account holder's name and balance, and methods for depositing and withdrawing money.

Java

class BankAccount {
    // Fields
    private String holderName;
    private double balance;

    // Constructor with a default balance of 0
    public BankAccount(String holderName, double balance) {
        this.holderName = holderName;
        this.balance = balance;
    }

    // Method to deposit money
    public void deposit(double amount) {
        if (amount > 0) {
            this.balance += amount;
            System.out.println(amount + " deposited. New balance: " + this.balance);
        } else {
            System.out.println("Deposit amount must be positive.");
        }
    }

    // Method to withdraw money
    public void withdraw(double amount) {
        if (0 < amount && amount <= this.balance) {
            this.balance -= amount;
            System.out.println(amount + " withdrawn. Remaining balance: " + this.balance);
        } else {
            System.out.println("Insufficient balance for the withdrawal or amount is not positive.");
        }
    }

    // Getter methods
    public String getHolderName() {
        return holderName;
    }

    public double getBalance() {
        return balance;
    }
}

class Solution {
    public static void main(String[] args) {
        BankAccount account = new BankAccount("Alex", 1000);  // An account with an initial balance of 1000

        account.deposit(500);  // Deposit money
        // Output: 500 deposited. New balance: 1500

        account.withdraw(200);  // Withdraw money
        // Output: 200 withdrawn. Remaining balance: 1300

        System.out.println("Final balance in " + account.getHolderName() + "'s account: " + account.getBalance());
        // Output: Final balance in Alex's account: 1300
    }
}

class BankAccount {
    // Fields
    private String holderName;
    private double balance;

    // Constructor with a default balance of 0
    public BankAccount(String holderName, double balance) {
        this.holderName = holderName;
        this.balance = balance;
    }

    // Method to deposit money
    public void deposit(double amount) {
        if (amount > 0) {
            this.balance += amount;
            System.out.println(amount + " deposited. New balance: " + this.balance);
        } else {
            System.out.println("Deposit amount must be positive.");
        }
    }

    // Method to withdraw money
    public void withdraw(double amount) {
        if (0 < amount && amount <= this.balance) {
            this.balance -= amount;
            System.out.println(amount + " withdrawn. Remaining balance: " + this.balance);
        } else {
            System.out.println("Insufficient balance for the withdrawal or amount is not positive.");
        }
    }

    // Getter methods
    public String getHolderName() {
        return holderName;
    }

    public double getBalance() {
        return balance;
    }
}

class Solution {
    public static void main(String[] args) {
        BankAccount account = new BankAccount("Alex", 1000);  // An account with an initial balance of 1000

        account.deposit(500);  // Deposit money
        // Output: 500 deposited. New balance: 1500

        account.withdraw(200);  // Withdraw money
        // Output: 200 withdrawn. Remaining balance: 1300

        System.out.println("Final balance in " + account.getHolderName() + "'s account: " + account.getBalance());
        // Output: Final balance in Alex's account: 1300
    }
}

In the BankAccount class, the fields holderName and balance are private, with public getter methods to retrieve these values. This organization emphasizes encapsulation and demonstrates how Java classes encapsulate data and behavior.