Methods and Fields

Introduction

Fields and Methods are fundamental components of a Java class.
Fields hold data, while methods define behavior.

Fields

Definition

Fields: Variables that store data for an object.
Also known as member variables or attributes.

Types of Fields

Instance Fields:
- Belong to an instance of a class.
- Each object has its own copy.
- Example:
```
public class Car {
    int speed;  // Instance field
}
```
Static Fields:
- Belong to the class, not any particular instance.
- Shared among all instances.
- Example:
```
public class Car {
    static int totalCars;  // Static field
}
```

Access Modifiers

Public: Accessible from any other class.
Private: Accessible only within the same class.
Protected: Accessible within the same package and subclasses.
Default (no modifier): Accessible within the same package.

Example

public class Person {
    private String name;  // Private instance field
    public static int population;  // Public static field
 
    public String getName() {  // Public method to access private field
        return name;
    }
 
    public void setName(String name) {  // Public method to modify private field
        this.name = name;
    }
}

Methods

Definition

Methods: Functions that define behavior and perform operations.
Can manipulate fields and perform operations on objects.

Types of Methods

Instance Methods:

Operate on instances of a class.
Can access instance fields and methods.

Example:

public class Car {
    public void drive() {  // Instance method
        // Code to drive the car
    }
}

Static Methods:

Belong to the class, not to any specific instance.
Can access static fields and methods only.

Example:

public class Car {
    public static void showTotalCars() {  // Static method
        // Code to display total number of cars
    }
}

Method Overloading

Method Overloading: Multiple methods with the same name but different parameters.
Enhances readability and functionality.

Example:

public class Calculator {
    public int add(int a, int b) {  // Method 1
        return a + b;
    }
 
    public double add(double a, double b) {  // Method 2
        return a + b;
    }
}

Access Modifiers

Same as fields: public, private, protected, and default (no modifier).

Example

public class Person {
    private String name;
 
    // Constructor
    public Person(String name) {
        this.name = name;
    }
 
    // Instance method
    public String getName() {
        return name;
    }
 
    // Static method
    public static void printPopulation() {
        System.out.println("Population: " + population);
    }
}

Summary

Fields store data and can be either instance-specific or shared (static).
Methods define behavior, can be overloaded, and can be either instance-specific or class-specific (static).
Proper use of access modifiers ensures encapsulation and security in your code.

Java Features Access Modifiers