Definition

A mutator method modifies an object’s state my changing the value of its fields or attributes.

Example:

Say you have an object called “Minion.” If I have a field like “name,” a mutator method lets me change its value.

Okay but why???

Mutator methods are part of Java’s philsophy of “encapsulation.”

That’s nerd-speak for “keeping things seperate”. It’s the idea of enclosing data and methods as a unit. You want to restrict direct access to data, only accessing them through a PROPERLY defined way.

Mutator method types:

Accessors: can you guess what this does? That’s right, it lets you access data. These can be called “get” methods or “getters.”

public class Minion
{
    private String name;

    // notice how the getter method starts with "get" (pretty creative, I know)
    // these methods have to be names like this where you have get<whatever variable>
    public String getName() {
        // because "name" is a string, return type is String
        return name;
    }
}

Your turn!

  • Make your own class with your own getter method

Mutators: wait a minute, a “mutator” is a type of mutator method??? Yeah, Java is kinda wacky like that. Try not to think about it much. Anyways… these methods let you mutate data (basically change it). They can be called “set” methods or “setters.”

public class Minion
{
    private String name;

    // same naming scheme as a getter but with set instead
    public void setName(String n) {
        name = n;
    }
}

Your turn!

  • Make your own class with your own setter method

EXAMPLE TIME WOOOOOOO!!!!!!! 🤓🤓🤓

public class Minion {
    // the minion's name
    private String name;

    // Constructor to set the name
    public Minion(String n) {
        name = n;
    }

    // getter
    public String getName() {
        return name;
    }

    // setter
    public void setName(String n) {
        name = n;
    }
}

// Create a Minion object and interact with it
Minion myMinion = new Minion("Kevin");

System.out.println(myMinion.getName()); // get the name

myMinion.setName("Bob");
System.out.println(myMinion.getName()); // wow look, the name changed!!


Kevin
Bob

Your turn!

Make your own class with:

  • A constructor
  • A getter
  • A setter

Create an object and interact with it! Make sure you use both your setter and getter methods at least once.

When making mutator methods…

  • A setter method has a void return type since it doesn’t return anything
    • Naming convention: set<variable name> like setName
  • A getter method’s return type is of what it is returning
    • Naming convention: get<variable name> like getName
  • Mutator methods in general change variable in a safe way
    • They have to be public if you want to access these variable outside of the class (which is the purpose they serve)
  • Parameter type matches the variable you’re modifying
    • public void setName(String n)
    • You are modifying a String called n
    • Parameter type matches!