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search specific data using ObjectInputStream

 
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On line 6 you have a Car list and a Car array, which is it? How was Car list/array written to the file in the first place?

We'd need to see the source for Car and the source for where the data was being written.
 
lee ji eun
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//this is my car class
 
Carey Brown
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You've got an array and and index into the array so data should be the i'th element in the array followed by getRegNum().
 
Carey Brown
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Carey Brown
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I would think you'd want to search the static Car[] in the class and not the file. If someone wants to search the file then they should call readFile() followed by a call to search(). Search should not be responsible for reading as well. The way you have it there is the potential with search to populate the array without populating nextId.
 
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Carey Brown wrote:You've got an array and and index into the array so data should be the i'th element in the array followed by getRegNum().


This will barf when the i'th element is null.
 
lee ji eun
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so i should write a method that search in the array ?
 
Carey Brown
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lee ji eun wrote:so i should write a method that search in the array ?

Yes, and avoid nulls.

 
lee ji eun
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sorry for the late reply. i will try it soon. thank you so much
 
lee ji eun
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//this is what i do but still cannot output anything
 
lee ji eun
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// this is my main program
 
Carey Brown
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lee ji eun wrote:

Line 3: Could "regNum" be null? possible but not likely. Even if it is null, checking it 100 times inside the loop isn't going to make a difference.

On the other hand (line 4) could carList[i] be null? Absolutely, even guaranteed.

"car" is a reference to a Car object. "carList" is an array of references to Cars. So after line 4, "car" now contains the same reference as carList[i]. You can test "car" to see if it's null and you can print "car" on line 5.
 
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You are trying to find the regNum so you would loop through the array, and check if the car value's regNum matches value you passed in.
 
lee ji eun
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yes, but i cannot output anything
 
Al Hobbs
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Have you tried debugging the app to see if you can find the problem?
 
Al Hobbs
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What exactly are you trying to do?
 
lee ji eun
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no i dunno how to do that
 
Al Hobbs
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What IDE are you using?
 
lee ji eun
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jcreator
 
Al Hobbs
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Which version are you using because LE doesn't have a debugger apparently.
 
lee ji eun
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JDK version 1.8.0_92
 
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If debugging is a problem why not add System.out.println() calls, printing out values so you can at least see what the flow is, and what value everything has.
 
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Al Hobbs wrote:Which version are you using

I presume you meant which version o JCreator not of the JDK.

. . . LE doesn't have a debugger apparently.

Does that mean JCreator Lite?
 
Al Hobbs
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It might be lite.   Either way i think learning how to use a debugger is worth it over just using print statements.  Still not really sure what hes trying to do with the code.
 
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Al Hobbs wrote:It might be lite.   Either way i think learning how to use a debugger is worth it over just using print statements.


There is one school of thought that considers skills with a debugger a Bad Thing. They prefer learning how to write unit tests that will fail when there's a bug in your code. Also, learning how to write tests up front so that you have a failing test if your code is missing some kind of functionality (you could also think of missing functionality as a "bug")
 
Al Hobbs
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How many tests are good to write?  Like one per public method or what is a good gauge to know if you have enough or too many?
 
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At least one per public method.  You should test all sorts of input and output.
 
Knute Snortum
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Here's a test of one method from an old project of mine.  Notice that it tests all sorts of behavior:
 
Carey Brown
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Consider Paul's rocket mass heater.
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