arraylist initialization error

Question

I have a problem with initializing ArrayLists.

When I used NetBeans 7.3 I tried to do this:

protected Stack<Scope> scopeStack;
protected ArrayList<Scope> allScopes;
scopeStack = new Stack<>();
allScopes = new ArrayList<>();

the file is perfectly compiled and goes fine.

But when I switch to linux using command line to compile java. It gives me an error

src/SymbolTable.java:28: illegal start of type scopeStack = new Stack<>();      
SymbololTable.java:29: illegal start of type allScopes = new ArrayList<>();

Is this cause by different versions of java compiler? Or what's the reason that cause this?

This is a Java 1.7 versus 1.6 error -- 1.6 doesn't have the <> "diamond" generic type-inference syntax. — Thomas W
– Thomas W, Commented Oct 11, 2013 at 22:00

Boris the Spider · Accepted Answer · 2013-10-11 21:59:22Z

10

I would conjecture that in Netbeans you are using Java 1.7 and on Linux you are using Java 1.6.

The "diamond operator" was only introduced in Java 7.

Use javac -version to see what version of the compiler your a running.

answered Oct 11, 2013 at 21:59

Boris the Spider

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Comments

BlackHatSamurai · Accepted Answer · 2013-10-11 22:33:07Z

2

You need to define the type when you initialize if you are using Java 6, like so:

scopeStack = new Stack<Scope>();
allScopes = new ArrayList<Scope>();

edited Oct 11, 2013 at 22:33

answered Oct 11, 2013 at 21:59

BlackHatSamurai

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5 Comments

Thomas W Over a year ago

In java 7 the <> "diamond" generic type-inference operator should avoid the need to specify the generic type, if it can be inferred. His problem is he's using Java 6 (or Java 6 output compatability) on the Linux compiler which fails.

BlackHatSamurai Over a year ago

@ThomasW Well first of all, we don't know that he is using Java 7, and if he isn't then he would have to infer it. I don't understand the downvote. If he is going from Java 7 to Java 6, then he would have to specify the type... I don't think it should be a downvote.

Thomas W Over a year ago

I took it, from a Java 7-specific syntax, he was using Java 7 (on the box that worked). See docs.oracle.com/javase/tutorial/java/generics/… and stackoverflow.com/questions/4166966/… for a discussion of this new syntax.

Andrew Barber Over a year ago

Blaine: reactions like yours here are why so many people never bother leaving comments with down votes. /cc @ThomasW

Sherwood Lee Over a year ago

Sorry for the confusion. In the beginning, I am not sure the version between linux and my computer is different. So I didn't imply that. Anyway, thank you all for answering this!!

Jon Newmuis · Accepted Answer · 2013-10-11 21:58:56Z

0

You should specify the type of your collection in your new call, and initialize the fields in the proper place. Try either:

Initializing the fields inline

protected Stack<Scope> scopeStack = new Stack<Scope>();
protected ArrayList<Scope> allScopes = new ArrayList<Scope>();

Initializing the fields in a constructor

public class MyClass {
  protected Stack<Scope> scopeStack;
  protected ArrayList<Scope> allScopes;

  public MyClass() {
    scopeStack = new Stack<Scope>();
    allScopes = new ArrayList<Scope>();
  }
}

answered Oct 11, 2013 at 21:58

Jon Newmuis

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1 Comment

Thomas W Over a year ago

Not relevant to his problem, incorrect in regards to the <> new Java 7 diamond syntax. I would agree with initializing in the declaration or constructor, though.

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