[Explained in Depth] How to Call a Method in Java

Methods are the essential building blocks in Java that enable code reuse, modularity, and abstraction. As a Java developer, having a deep understanding of how to properly declare, define, and call methods is crucial.

In this comprehensive 4500+ word guide, I will cover everything you need to know about methods in Java. We‘ll start from the basics, explore common method-related concepts, go over method syntax in detail, look at examples, and finish with best practices and tips for writing solid methods.

Grab a nice cup of coffee and let‘s dig in!

What Exactly is a Method in Java?

Let‘s begin with a high-level overview of what methods are in Java.

A method is a collection of code statements grouped together to perform a specific task. It provides a way to compartmentalize parts of a program.

Methods have the following key characteristics:

Reusability – Methods let you reuse code without rewriting it. Just call the method whenever you need the logic.
Modularity – Methods promote modular programming style. Code is organized into logical, distinct sections with clear interfaces.
Abstraction – Methods hide complex implementation details. The code inside the method is abstracted away.
Information hiding – Methods expose only what‘s necessary and keep the rest private. This reduces complexity and dependencies.

So in essence, a method takes input, performs defined computations, and optionally returns output. By encapsulating code into reusable methods, programs become easier to develop, read, maintain, and debug.

Why Using Methods is Recommended

Here are some key reasons why using methods is highly recommended when programming in Java:

Reusability – Extracting reusable code into methods avoids duplication. This saves time and reduces bugs.
Modularity – Breaking code into methods organized by functionality results in modular, compartmentalized code that is easier to navigate and change.
Maintainability – Methods let you isolate and change implementation details without impacting calling code. This makes maintenance and testing easier.
Readability – Small, appropriately named methods are easier to understand compared to monolithic code. Descriptive method names act as documentation.
Abstraction – Methods allow working with complexity at higher levels without getting caught in implementation details. This enables better focus on problems you are solving.
Information hiding – Methods only expose essential details to other code. Important data and implementation can remain safely encapsulated and private.

Writing code with properly scoped methods leads to systems that are more extendable, adaptable, and scalable. That‘s why methods are so integral to object-oriented languages like Java.

Types of Methods in Java

There are two broad categories of methods in Java:

Instance Methods

Instance methods are defined in a class and belong to an instance or object of that class.

To call an instance method, you first need to create an object using the new keyword. Then you can invoke the method on that object reference.

For example:

MyClass myObject = new MyClass(); 
myObject.instanceMethod();

Instance methods can access the internal state of the object and work with data stored in object attributes.

Static Methods

Static methods belong to the class itself rather than any instance. They are scoped at the class level.

Static methods can be invoked directly using the class name without needing to instantiate the class.

For example:

MyClass.staticMethod();

Static methods are limited in that they cannot access non-static class members directly.

Knowing when to use static vs instance methods is an important design decision when modeling classes.

Method Declaration Syntax in Java

The syntax for declaring a method in Java is as follows:

modifier returnType name(parameterList) {
  // method body
}

Let‘s examine each component:

Modifier – Optional, specifies visibility as public, private, protected or default (package-private).
Return type – The data type of value returned by the method, or void if no return value.
Name – Unique identifier for the method, following camelCase naming convention.
Parameter list – Comma-separated list of input parameters and their types. Empty parentheses if no parameters. Can use varargs.
Method body – Contains the executable statements surrounded by { } that define what the method does.

For example, a basic method declaration might look like:

public double calculateAverage(int[] numbers) {
  // method body
}

This defines a public method named calculateAverage that accepts an int[] as input and returns a double result.

Let‘s look at some method components and syntax rules more closely.

Specifying the Method Access Modifier

The access modifier defines the visibility of the method from other code. Java has four possible access levels:

public – Accessible from any class. Most common for methods.
protected – Accessible within the package and subclasses. Used less frequently.
private – Only accessible within the declaring class itself. Used when you want strict encapsulation.
Default (package-private) – No modifier. Available to classes in same package only.

Access can be narrowed step-by-step from public down to private. Once code accesses a method, it will continue to have access at the same or broader scope.

Appropriate access level depends on your design. Use the most restrictive level possible based on requirements.

Understanding Method Return Types

The method‘s return type declares the data type of value returned when the method is called. Let‘s explore method return types further:

Primitive return types – Methods can return primitive data like int, double, char, boolean.
Object return types – Methods can return object instances of any class or interface type.
Void return type – void is used when a method does not return any value.
Generic return types – Return type can be a generic like T to allow flexible return values.

The return type is mandatory (except for constructors which implicitly return the constructed object instance).

Return types define what callers can do with the method result. Proper return types increase understandability.

Working with Method Parameters

Parameters allow passing arguments to a method when invoked so it can operate on the given inputs. Here are some key points about method parameters:

Input parameters – Used to pass data into the method. Parameters define name and type.
Varargs – Varargs (variable arguments) parameter indicates the method accepts variable number of arguments.
Default values – Parameters can specify default value which is used if no argument passed.
Parameter validation – Good practice is to validate parameters at start of method body before use.
Local variables – Method can also define its own temporary local variables that exist only within the method scope.

Well-defined parameters that validate input and have descriptive names clarify method usage.

Understanding Static vs Instance Methods

The choice between static and instance methods depends on whether it logically makes sense for the method to be tied to class or object state:

Use static methods when functionality is not related to any particular object instance. For example, utility methods that perform general computations.
Use instance methods when functionality needs access to internal object state. For example, methods that operate with object attributes.

Instance methods can use this keyword to reference the current object instance. Static methods can interact with static class variables and call other static methods.

Switching a method that accesses state between static and instance will break functionality, so choose carefully!

Leveraging Method Overloading in Java

Java enables method overloading – providing multiple methods with the same name but different parameters.

The compiler knows which overloaded variant to call based on the parameter types used in the method invocation.

For example:

public class Calculator {

  public int add(int x, int y) {
    return x + y; 
  }

  public double add(double x, double y) {
    return x + y;
  }

}

This Calculator class has two add() methods that take different parameter types. We can call either version as needed:

Calculator calc = new Calculator();

int sum1 = calc.add(1, 2); // Calls int version  

double sum2 = calc.add(1.5, 2.5); // Calls double version

Overloading is useful when you want the same logic applied to different types. It avoids code duplication and improves readability.

Understanding Variable Argument Methods

A varargs (variable arguments) parameter allows passing a variable number of arguments to a method.

To declare a varargs parameter, use an ellipsis ... after the parameter‘s base type:

public void printMessages(String... messages) {
  // method body
}

When invoking a varargs method, you can pass:

Zero or more values
An array

Varargs match very flexibly with arguments:

printMessages("Hello"); // 1 argument

printMessages("Hello", "World"); // 2 arguments 

String[] messages = {"Hi", "Hey"};
printMessages(messages); // Pass array

The varargs automatically adapts to however many arguments are provided of matching type. Super convenient!

Understanding Recursive Methods in Java

A recursive method is one that calls itself repeatedly to perform an operation. Recursion is very useful for tasks like sorting, file system traversal, and complicated mathematical calculations.

Here is an example of a recursive method to compute factorial:

public int factorial(int num) {
  if (num <= 1) { 
    return 1;
  }

  return num * factorial(num - 1);
}

This method calls itself with num - 1 until the base case of num == 1 is reached. Recursion saves coding effort here versus using iteration.

Recursive methods must have a termination condition that does not lead to further recursion, otherwise an infinite recursive loop will occur!

How to Call Static Methods in Java

Calling a static method is easy – just reference the method name prefixed with the class name:

ClassName.staticMethodName(args);

Because static methods belong to the class itself, you can invoke them without needing an object instance.

For example:

public class MathUtils {

  public static int add(int x, int y) {
    return x + y; 
  }

}

public class Main {
  public static void main(String[] args) {  
    int sum = MathUtils.add(5, 3); // Invoke static method
    System.out.println(sum); // Prints 8
  }
}

The add() method is declared static in MathUtils, so we can call it directly via the class. Nice and easy!

How to Call Instance Methods in Java

To call an instance method, you first need to instantiate the class using the new keyword. Then you can invoke the method on the object instance:

ClassName objectRef = new ClassName();
objectRef.instanceMethod(args);

For example:

public class Calculator {

  public int add(int x, int y) {
    return x + y;
  }

}  

public class Main {
  public static void main(String[] args) {  
    Calculator calc = new Calculator(); // Instantiate class

    int sum = calc.add(5, 3); // Call instance method
    System.out.println(sum); // Prints 8
  }
}

Here we instantiate Calculator before calling add(). Instance methods operate on object state.

Common Errors When Calling Methods in Java

While calling methods is straightforward, here are some common mistakes to avoid:

Forgetting the new keyword when invoking an instance method – will give a NullPointerException error. Always instantiate first!
Using the wrong number or type of arguments – causes a compile-time error. Double check parameters match.
Forgetting to import the class – leads to compiler being unable to find the class and method. Don‘t forget the imports!
Catching exceptions but failing to handle them – can leave code in invalid state. Make sure to handle exceptions.

Carefully validating arguments and handling exceptions makes method calls more robust and prevents bugs!

Best Practices for Writing High Quality Methods

Let‘s cover some key best practices I recommend using when defining your own methods:

Use descriptive names – Method names should clearly convey what the method does, like calculateTotal() rather than calc().
Follow conventions – Stick to standard Java naming and style conventions and patterns. This will make your code more familiar.
Keep methods short – Methods should focus on one coherent task. Extract complicated workflows into multiple methods.
Validate arguments – Do parameter validation at the start of the method body and throw exceptions for invalid data.
Avoid side-effects – Where possible, don‘t modify state – have methods return results rather than tweak global values.
Minimize accessibility – Only make methods public when truly necessary. Use access modifiers like private whenever possible.
Write docs – Taking time to write Javadocs clarifying method behavior pays off when reading code later.
Handle errors – Catch exceptions properly and include error handling logic rather than ignoring issues.

These practices will result in professional, production-quality methods that enhance your overall application design.

Key Takeaways

We‘ve covered a ton of ground here! Let‘s recap the key points:

Methods encapsulate reusable code segments that promote modularity and abstraction.
Instance methods operate on object state while static methods don‘t.
Method parameters and return types define interface and usage.
Overloading allows same method name with different parameters.
Varargs provide flexible argument handling.
Follow naming conventions and validation best practices.
Carefully choose visibility using access modifiers.

Mastering methods will elevate your Java skills far beyond novice level. I hope this guide gave you a deep understanding of methods from basic principles to nuanced details! Let me know if you have any other method-related questions.