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  1. #1
    jwl
    jwl is offline Member
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    Default Instance variables

    Hello,

    I am going through "Java Concepts 6th Edition" by Cay Horstmann and I am having trouble With creating a new counter and a couple of other things. Here is the code from chapter 3.

    Java Code:
    import sun.management.counter.Counter;
    
    public class counter {
            private int value = 4;
            Counter tally = new Counter(); //Error Counter is Abstract; cannot be instantiated
            tally.count();                 //Error package tally DNE
            tally.count();                 //Error packege tally DNE                         
            int result = tally.getValue(); //Error Incomparable types required int
                                           //      found java.lang.Object
            public void count(){
                value = value + 1;
            }  
            
            public int getValue() {
                return value;
            }
        }
    I think I know why the tally isn't working(this is all the code I have for this problem) but I don't know why the counter isn't working since I did something similar to this in chapter 2.

    Java Code:
    // from chapter 2
    JavaApplication63 component = new JavaApplication63();
            frame.add(component);
    Can someone please help with this

  2. #2
    quad64bit's Avatar
    quad64bit is offline Moderator
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    Default Re: Instance variables

    Why do you have a class called "counter" and a class you import called "Counter"? Java is case sensitive, and class names should never be lower case. I also don't understand how this code even compiles, since you cannot call methods outside of a method body...

  3. #3
    SJF
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    Default Re: Instance variables

    Well, for staters if Counter is an abstract class, you'll have to create a class that implements Counter, and instantiate that class...

    Java Code:
       public class MyCounter implements Counter{
    ....
    }
    ALL abstract methods in Counter then need to be properly implemented.

    Java Code:
    			@Override
    			public int getFlags() {
    				throw new UnsupportedOperationException();   //or return 0; or return -2000; doesn't really matter
                                                                                                   //what does matter is that the abstract methods are implemented.
    			}
    You will instantiate YOUR class...
    Java Code:
        Counter tally = new MyCounter();

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