When should I use "this" in a Java class?

java

object-oriented-programming

best-practices

java-basics

byAnton Shumikhin·Oct 8, 2024

You'll find this particularly handy in Java when:

Resolving identifier conflicts: When local variables overlap with instance fields. this clearly highlights which is which, especially in setters and constructors:

this.field = field;

Referring to the instance itself: If you need to mention the current object within class methods or need to pass it to some other method.
Chaining constructors: When you want to invoke a constructor from another using this(argument list).

public Example() {
    this(42); // initializing using 'this'
}

Apply this wisely and tactically:

public class Example {
    private int value;

    public Example(int value) {
        this.value = value; // No more hit or miss. It's definitely the field, not the parameter.
    }
}

Your Swiss army knife: "this"

When traversing the jungle of Java, this is your Swiss army knife. Here's a rundown of its utility:

Initialization: More than meets the eye

Using this gently avoids shadowing when a local variable and an instance variable share names:

public void setName(String name) {
   this.name = name; // It's 'name', but make it instance
}

Object state changes: Now you're changing!

Use this to express that your code is set to transform an object:

public void register() {
   EventBus.register(this); // Hey EventBus, look what I got!
}

Nested classes: Talking to the outer self

To access the outer class's members from a nested class, embrace Outer.this. It's intimacy at its finest:

class Outer {
    int value;
    class Inner {
        void updateValue() {
            Outer.this.value = 30; // 20 is so 2020. Let's make it 30.
        }
    }
}

Because readability counts

Even when not obligatory, this can boosts readability to new heights:

public void increment() {
    this.count++; // 'count' without 'this' is like a burger without fries 😋
}

Visualization

Picture this as a mailbox:

class House {
  String color;
  void repaint(String color) {
    color = color; 
    // Uh-oh! It’s like posting a letter to a street name. 📬❌

    this.color = color; 
   // Ding! The post goes straight to your inbox. 📬✅
  }
}

The right address: Specify your address as this.color, or you might end up coloring someone else's house. Yikes! 💡

Unleashing the power of "this"

To utilize Java at its fullest, one needs to realize that this is not just a reference. It's an ode to OOP. Here's how you can exploit this fully:

Method invocation odyssey

To make it explicit that a method invocation is happening on the current object, this is the hero. This especially shines when dealing with overlapping scopes:

public void display() {
    this.initialize(); // On Wednesdays we initialize
}

Romeo and Juliet in OOP world

In larger projects with different coding conventions, or when your variable names clash with Java keywords, this can play the role of a peace marker and enhance clarity:

public class Counter {
    int count;
    public Counter(int count) {
        this.count = count; // This 'count'? That 'count'? Oh, 'this' count!
    }
}

In your IDE we trust

Using this. smoothly sails the IDE's intellisense to where you want it to go:

this.username = ...; // And the IDE goes: "Gotcha buddy!"

Reflexive calls: Choose yourself

For passing this when setting up listeners or handlers, choose this.handleClick(). It’s never vain to choose yourself.

button.setOnClickListener(v -> this.handleClick()); 
// Just happened to pass by and clicked myself. Casual stuff.

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