Skip to content

This

Every object has a reference to itself: this.

An object can use this to refer to its own fields and methods.

public class Account3 {
  private double balance;
  private String accountId;

  public Account3(String aId) {
    accountId = aId;
    // this to call a method
    this.setBalance(0.0);
  }

  //...

  public void setBalance(double bal) {
    // this to access a field
    this.balance = bal;
  }
  //...
}

this and Scope

Recall that scope is the { } in which a variable lives.

What if we have a class designed like Account4?

public class Account4 {
  private double balance;
  private String accountId;

  public void setBalance(double balance) {
    balance = balance;
  }
  //...
}

This setter does not set the balance field.

  • Instead, it is setting the balance parameter of the setBalance method.

  • balance = balance; is redundant.

The reason for this is scope: because we have a parameter balance in the setBalance method, Java assumes that's what we're referring to when we write balance = balance;, not the balance field.

  • We call this shadowing: inside setBalance the parameter name shadows the field name.

shadowing

A local variable, with the same name as a field, having scope that overlaps the field's scope. When we use the name, the local variable is used. It's as if it casts a shadow over the field so that Java can't see the field anymore.

Shadowing

We can qualify which balance we mean by using this.

public void setBalance(double balance) {
  this.balance = balance;
}
* This code sets the field balance to the value in the parameter balance.

Shadowing

Drill

Encapsulation/com.example.encapsulation.drills.Account * Change the class to use this. in the setter methods. * Rename your setter parameters the same as your fields. * Run BankApp to verify everything still works.

Prev -- Up -- Next