Why use 'while' and were place it and how finish the challenge?

Question

Okay, dear reader, I'm full of questions again :-)... but willing to solve it! First question: do I use while (instead of if) because I don't know where the loop ends? (Should I use if, when it says: it has to charge at a stage of 4; so it is a special number?)

Do I have to place the 'while loop' at the public boolean isFullyCharged? or (like I did) near the other part with 'charge'? And how do I normally know where to place an extra code....

I think I wrote: while it is not fully charged (!isFullyCharged()), then put 1 extra to it (mBarsCount ++), but it doesn't work, so I think I'm missing something.

Please can someone help me out? Thanks!

GoKart.java

public class GoKart {
  public static final int MAX_ENERGY_BARS = 8;
  private String mColor;
  private int mBarsCount;

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

  public String getColor() {
    return mColor;
  }

  public void charge() {
    mBarsCount = MAX_ENERGY_BARS;
    while (!isFullyCharged()){
mBarsCount ++;
    }
  }

  public boolean isBatteryEmpty() {
    return mBarsCount == 0;
  }

  public boolean isFullyCharged() {
    return mBarsCount == MAX_ENERGY_BARS;
  }

}

Answer 1 · 2016-02-04T13:25:54Z

February 4, 2016 1:25pm

Hi Jari,

You can use a while loop when you don't know how many times, or if at all, you want to loop through a set of code. Th loop iterates while a certain condition is, or is not, in place. The condition may exist already, so the loop won't run, or it may never occur, so the loop will continue forever. Usualy, you add a control mechanism into the loop so you make sure the loop will stop at some point, but that isn't necessary; some things are meant to persist permanently, perhaps. An if statement tests something once, a loop tests it as many times as is necessary. If you do know how many iterations you want, such as iterating over the contents of an array of known length, you can use an alternative for loop.

In your code, you have controlled the while loop well. Your test is correct and you will increment mBarsCount until isFullyCharged returns true. In isFullyCharged you are testing to see if mBarsCount holds a value equal to MAX_ENERGY_BARS. So, there's no need for the line in your code that assigns the value of MAX_ENERGY_BARS to mBarsCount - that is why you are incrementing in the first place.

So your loop carries on until mBarsCount equals MAX_ENERGY_BARS through the use of the helper method isFullyCharged. The while loop replaces the assignment of MAX_ENERGY_BARS. Your charge method will look like:

  public void charge() {
    while(!isFullyCharged()){
      mBarsCount++;
    }
  }

I hope that helps.

Steve.

Answer 2 · 2016-02-04T12:42:06Z

February 4, 2016 12:42pm

Yes, use while, if you were to use an "if" statement, the code inside the block would only run once, and increment the variable only once.
Your while loop is correct. It is basically saying "while NOT fully charged, keep adding energy bars". Once it is full, then set the mBarsCount to MAX_ENERGY_BARS.
You're really close. The problem is that your while loop should come before the assignment.

    while (!isFullyCharged()){
         mBarsCount ++;  // no space before ++
    }
 mBarsCount = MAX_ENERGY_BARS  // unnecessary line and omitted trailling ;

[MOD: added correction comments]

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Jari Koopman

Jari Koopman

Why use 'while' and were place it and how finish the challenge?

2 Answers

Steve Hunter

Steve Hunter

Jari Koopman

Jari Koopman

Steve Hunter

Steve Hunter

Rajen Tandel

Rajen Tandel

Jari Koopman

Jari Koopman