Top Ten Errors Java Programmers Make

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25 Oct 10

Larry Crosswell

Great article to help you avoid or find your mistakes

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24 Oct 10

Cinzia Bocchi

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03 Sep 10

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static methods (such as main)
signature
marked static - meaning that we don't need to create an instance of the class
public String my_member_variable
my_member_variable
If you want to access
member variables from a non-static method
you must create an instance of the object
NonStaticDemo demo = new NonStaticDemo();
demo.my_member_variable );

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19 May 10

alashe

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putrakopo

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02 Feb 10

Lance Pedersen

demo = new NonStaticDemo();
demo.
Comparison assignment ( = rather than == )
objects
to see if they point to the same object.
we are actually comparing two object references
.equals method, which is a method inherited by all classes from java.lang.Object.
if ( (abc + def).equals("abcdef") )
When you pass a primitive data type
passing by value. That means that a copy of the data type is duplicated, and passed to the function. If the function chooses to modify that value, it will be modifying the copy only.
When you pass a Java object, such as an array, a vector, or a string, to a function then you are passing by reference. Yes - a String is actually an object
Any changes you make to the object's member variables will be permanent - which can be either good or bad, depending on whether this was what you intended.
Java is zero-indexed
Just like the ArrayOutOfBoundsException, there is a string equivalent. Accessing beyond the bounds of a String will cause a StringIndexOutOfBoundsException to be thrown, as demonstrated by this example.
all methods and member variables in the Java API begin with lowercase letters
all methods and member variables use capitalization where a new word begins e.g - getDoubleValue()

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23 Dec 09

Bruno Ferreira

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Accessing non-static member variables from static methods (such as main)
Mistyping the name of a method when overriding
Comparing two objects ( == instead of .equals)
When you pass a primitive data type, such as a char, int, float, or double, to a function then you are passing by value
When you pass a Java object, such as an array, a vector, or a string, to a function then you are passing by reference
I know it's very tempting to write blank exception handlers, and to just ignore errors. But if you run into problems, and haven't written any error messages, it becomes almost impossible to find out the cause of the error.
Forgetting that Java is zero-indexed
Preventing concurrent access to shared variables by threads
Capitalization errors
1. Null pointers!

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24 Aug 09

mel pullen

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28 Jul 09

rinaldi fonseca

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18 Jun 09

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13 May 09

Aaron Law

program regularly in Java, and know it like the back of your hand, or whether you're new to the language or a casual programmer, you'll make mistakes. It's natural, it's human, and guess what? You'll more than likely make the same mistakes that others do, over and over again. Here's my top ten list of errors that we all seem to make at one time or another, how to spot them, and how to fix them.

07 May 09