Time estimate: 45 min.

5.9. this Keyword

The keyword this can be used in a class to refer to the current calling object.

For example, in the following Class Person, when we create an object p1 and call the constructor or p1.setEmail(), the word “this” refers to p1. And when we make the same method calls with object p2, “this” refers to p2. Run the code below and also check it out in the Java visualizer with the Show CodeLens button which shows how this refers to different objects when the code is run.

Observe the use of the keyword this in the code below. Click on the CodeLens button and then forward to see the memory in action.


Note that in the code above, this.name, this.email, and this.phoneNumber are equivalent to writing just name, email, and phoneNumber, but this.variable is a way to indicate that we are referring to the instance variables of this object instead of a local variable.

Static methods cannot refer to this or instance variables because they are called with the classname, not an object, so there is no this object.

The keyword this is sometimes used by programmers to distinguish between variables. Programmers can give the parameter variables the same names as the instance variables and this can distinguish them and avoid a naming conflict. For example, both the instance variable and the parameter variable are called name in the code below.

// instance variables
private String name;

// constructor
public Person(String name)
   // Set this object's instance variable name to the parameter variable name
   this.name = name;

The this variable can be used anywhere you would use an object variable. You can even pass it to another method as an argument. Consider the classes below, Pay and Overtime. The Pay class declares an Overtime object and passes in this (the current Pay object) to its constructor which computes the overtime with respect to that Pay object. Try this code in the active code exercise below with the Show CodeLens button to trace through it step by step. Here is an image that shows how this, myPay and p all refer to the same object in memory.


What does this code print out? Trace through the code with the Show CodeLens button. Notice how the this Pay object is passed to the Overtime constructor.

exercise Check Your Understanding

5.9.1. groupwork Programming Challenge : Bank Account


A bank account can be used to store your money. The bank keeps track of the account holder’s name, the acount balance which is the amount of money in the account, and assigns an account number to each account. At the bank or an ATM (automatic teller machine) or on a phone app, the account holder can deposit (add) or withdraw (subtract) an amount from their account. Here’s a video that shows the steps to use an ATM to withdraw money from a bank acount. Phone apps like Venmo and Paypal connect to your bank account or credit card to send and get money from businesses or friends.

For this challenge, you can work in pairs to:

  • Create a class called BankAccount below that keeps track of the account holder’s name, the account number, and the balance in the account. Make sure you use the appropriate data types for these.

  • Write 2 constructors for the class: one that initializes all the instance variables and one that only has 2 parameters for the name and account number and initializes the balance to 0. For the parameters, use the same variable names as your instance variables. Use the this keyword to distinguish between the instance variables and the parameter variables.

  • Write a toString method for the class. Use the this keyword to return the instance variables.

  • Write withdraw(amount) and deposit(amount) methods for the class. The withdraw method should subtract the amount from the balance as long as there is enough money in the account (the balance is larger than the amount). And deposit should add the amount to the balance. Use the this keyword to refer to the balance.

  • Test your class below with a main method that creates a BankAccount object and calls its deposit and withdraw methods and prints out the object to test its toString method.

Create a class called BankAccount that keeps track of the account holder’s name, the account number, and the balance in the account. Create 2 constructors, a toString() method, and withdraw(amount) and deposit(amount) methods. Use the this keyword in the constructor and methods. Test your class in a main method.

5.9.2. Summary

  • Within a non-static method or a constructor, the keyword this is a reference to the current object, the object whose method or constructor is being called.

  • this.instanceVariable can be used to distinguish between this object’s instance variables and local parameter variables that may have the same variable names.

  • Static methods do not have a this reference.

  • The this variable can be used anywhere you would use an object variable, even to pass it to another method as an argument.

5.9.3. AP Practice

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