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

Answer 1

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.

Answer 2

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 ;)

Answer 3

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);
}});

Answer 4

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!

Answer 5

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;

    }