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Java Java Objects (Retired) Harnessing the Power of Objects Methods and Constants

Posted by James Pask
James Pask
13,600 Points

Stuck on challenge 3 of the "Methods and Constants challenge" on Java Objects..

On this part:

Finally, let's add a method named charge. It should be public and return nothing. When called it should set mBarsCount to the value of the constant you declared in Task 1.

I've attempted to add the part about it returning nothing and I think that "void" should be used somewhere but I can't get it to work. I'm having problems converting the string to an integer. Considered using the Interger.parseInt thing but couldn't get that to do anything sensible either - maybe I was just making up code?

Can someone point me in the right direction please?

GoKart.java 
public class GoKart {
  private String mColor;
  public static final int MAX_CHARGE = 8;
  private int mBarsCount;

  public GoKart(String color) {
    mColor = color;
    mBarsCount = 0;

  }

  public String getColor() {
    return mColor;
  public String charge;
     return mBarsCount;
  }
}

2 Answers

Steve Hunter
Steve Hunter
57,712 Points

OK - step by step:

Question: add a method named charge. It should be public and return nothing.

That looks like:

public void charge(){

}

Next up is the body of the method: When called it should set mBarsCount to the value of the constant you declared in Task 1.

public void charge(){
   mBarsCount = MAX_CHARGE;
}

You have the method declaration returning a String and then the method body returning the mBarsCount integer; it doesn't need to return anything. You also need to make sure that the method is declared with brackets after the name - they are empty as the method takes no parameters, but they are needed. And then you need to open up the body with a curly brace, and close that after the method.

Hope that makes sense!

Steve.

James Pask
James Pask
13,600 Points

I think it's starting to make sense. So, this code:

  public GoKart(String color) {
    mColor = color;
    mBarsCount = 0;
  }

is a method. And the code that we added in task 3 is also a method. Methods are applied to the variables of the class whereas "constructors" apply to the class itself, right?

Here is my finished code (which was accepted by the challenge (excluding my comments which I've added to help with my learning)).

If someone could also double check to ensure that my comments are correct, it'd be appreciated.

public class GoKart {
  // These variables apply to EVERY kart!
/** Yes they do! **/
  private String mColor;
  public static final int MAX_CHARGE = 8;
  private int mBarsCount;

  public GoKart(String color) {
    // The colour can be changed, as can the initial charge
/** the color is passed into the constructor so each kart can be individual, the mBarsCount is set (initialized) to zero for all **/
    mColor = color;
    mBarsCount = 0;
  }

  public void charge() {
    // Whatever happens, the charge can never exceed the maximum of 8.
/** calling the charge method will set mBarsCount to be MAX_CHARGE **/
    mBarsCount = MAX_CHARGE;
  }

  public String getColor() {
    // Expose the colour value from the kart
/** perfect, yes. mColor is private - this allows access to it indirectly - a 'getter' method **/
    return mColor;
  } 
}
Steve Hunter
Steve Hunter
57,712 Points
Steve Hunter
Steve Hunter
57,712 Points

Hi James,

I'm pretty sure you've got that, yes. There's some further learning to be done as the course progresses but you're pretty much on track.

A couple of points: "Methods are applied to the variables of the class" - methods can do anything they like. Very often, they manipulate the instance variables as you have pointed out. You'll do more with "getters and setters" as the course progresses which will reinforce what you've understood so far. Next, " "constructors" apply to the class itself" - not quite. A constructor creates the instance of the class. It can take parameters to build the instance, in this case the colour of the Kart object. So, the constructor is the code that is applied to all instances of the class to create those instances and enable to user to specify any unique features, color in this case.

I've added some alternative comments in response to your request too.

Hope that helps!

Steve.

James Pask
James Pask
13,600 Points

Appreciate your comments - thanks very much :)