Why does Eclipse require me to set (arbitrary) brackets in java code?

Question

I am currently trying to figure out how to use Eclipse to program Escape models in java. I am quite new to Escape and Eclipse, and it has been a while since I programmed in java, so please excuse if this is a stupid question.

Basically, I have been haunted by strange Eclipse error messages. I tracked the last one down to this problem:

This works:

public class CoordinationGame extends Scape {

.
    .
    .
    Scape lattice;

boolean test;
int test2;

{
test = true;
test2 = 3;
}

{
lattice = new Scape(new Array2DVonNeumann());
}

}

This gives strange error messages:

public class CoordinationGame extends Scape {

    .
.
.

Scape lattice;

boolean test;
int test2;

test = true;
test2 = 3;

lattice = new Scape(new Array2DVonNeumann());
}

i.e. { expected afer int test2 and Syntax error on token "lattice", VariableDeclaratorId expected after this token.

As I said, Java has been some time, but IIRC, those brackets should not be required. This question establishes that this bracket usage is an initializing block, but this is probably not what I want to do here.

Does anyone know why Eclipse requires me to set these brackets, or what I could do to change this behaviour?

Thanks in advance! Martin

PS: Some information that will probably be useful:

I use eclipse-indigo, installed the modelling toolkit AMP. I am not entirely sure how to check this, but I believe I am using jre6, as this is what it says in the JRE System Library tab of my package explorer. In the future, I plan to find a way to run the Escape modelling environment with Groovy, but that will be another question …

Please clean up. There is a much smaller example that would illustrate your question. — Urs Reupke, Jul 11 '11 at 09:44

Sean Patrick Floyd · Accepted Answer · 2011-07-11T09:49:23.083

5

This has nothing to do with your IDE. Java does not allow statements at class level, it does however allow initializers at class level.

{foo();}

This is an instance initializer, it will be copied into all constructors by the compiler.
(See Java Tutorial > Initializing Fields)

In Java, you can write statements in

a method
a constructor (which is a special kind of method)
an initializer block (static or instance)

but nowhere else.

edited Jul 11 '11 at 09:49

answered Jul 11 '11 at 09:41

Sean Patrick Floyd

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Alright, thank you. Is this behaviour new? In fact I wonder why the Escape tutorial does not know this. – mzuba Jul 11 '11 at 09:54
1

That has more or less been the behavior since day once of Java. – Martin Peters Jul 11 '11 at 10:25

score 3 · Answer 2 · answered Jul 11 '11 at 09:52

If you separate field initialization from declaration, you need a method or an initializer. This instance works without initializers:

package ede.brook.model;

import org.ascape.model.Scape;

public class CoordinationGame extends Scape {

    public int latticeHeight = 30;
    public int latticeWitdh = 30;
    public int nPlayers = 200;

    Scape lattice  = new Scape(new Array2DVonNeumann());;
    Scape players;

    boolean test = true;
    int test2 = 3;

    test = true;
    test2 = 3;

}

If an initializer is present, they are executed before the constructors.

As for coding practice, I would recommend against initializers and use a combined declaration + initialization for simple cases or (parameterless) constructors for more complicated constructs. An exception are static initializers, which may be necessary for more complex initializations:

static SomeTypeWithComplexInitialization staticField;

static {
  SomeOtherType factoryParameter = new SomeOtherType()
  staticField = SomeTypeFactory.createInstance(factoryParameter);
}

The only other instance where I would recommend using initializers are APIs that specifically recommend this. For example, JMock uses this syntax to provide an easy-to-grock lambda-like construct:

context.checking(new Expectations() {{
    oneOf (subscriber).receive(message);
}});

score 1 · Answer 3 · answered Jul 11 '11 at 09:44

public class CoordinationGame extends Scape {    
  // ...
  int test2;
  // ...
  test2 = 3;  // <- errror
}

This is illegal, we can't assign values this way in a class body. The other code was legal because you used a static initializer to init the field test2.

The error message is pretty misleading but, honestly, that happens quite often in Java ;)

score 0 · Answer 4 · answered Jul 11 '11 at 09:42

If you want to initialize the test and test2 variables you should do so at the point of declaration.

boolean test = true;
int test2 = 3;

The { and } you have added make an initializer block which avoids the error. It's a bit of an odd way to do things, so I'd always prefer to see variables initialized at the point of declaration if that's possible!

score 0 · Answer 5 · answered Jul 11 '11 at 09:46

If you want to initialize the fields lattice, test and test2, try using the following:

    package ede.brook.model;

    import org.ascape.model.Scape;

    public class CoordinationGame extends Scape {

    private static final long serialVersionUID = 1L;

    public int latticeHeight = 30;
    public int latticeWitdh = 30;
    public int nPlayers = 200;

    Scape lattice = new Scape(new Array2DVonNeumann());
    Scape players;

    boolean test = true;
    int test2 = 3;

    }

Why does Eclipse require me to set (arbitrary) brackets in java code?

5 Answers5

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