Can someone explain to me why I'm having this error?

Question

Good day,

I have a question on which in my code, one declaration is having an error outside a function.

The snippet is:

public class Gold {

    Block[][] block = new Block[4][4];


        this.block[1][4] = new Block(); //1


        public void populate() {
            this.block[1][4] = new Block();//2
    }

}

The code this.block[1][4] = new Block(); number 2 is not having an error. However, the first code which is not inside the function is showing the error:

Illegal start type

Cannot find symbol

']' expected

invalid method declaration, return type required.

I just want to understand why this is hapenning and what I am missing.

Thanks

Answer 1

没有索引为4的元素。最后一个元素的索引为3。

Answer 2

You can not initialize variables directly as you did above in case 1, You can initialize block[][] in constructor like :

public Gold(){
    this.block[1][3] = new Block();
}

OR in block like :

Block[][] block = new Block[4][4];
{
      this.block[1][3] = new Block();
}

Answer 3

You have a statement which must be in a block of code.

Try

public class Gold {
    Block[][] block = new Block[4][4];
    { // initializer block
        this.block[1][3] = new Block(); //1
    }

Answer 4

You have two problems here, You need to initialize any object in a scope. Either you have to call the Number 1 line in a constructor or in a function or with in a block (enclosed with in { and } ) . Here you need to know difference between static block and non-static blocks .

Other problem you have is this.block[1][4] = new Block(); will throw an ArrayIndexOutofBounds exception as the length of the array is 4 and you are trying to insert and object at 5th place.

Answer 5

I think that you should place your code in constructor:

public Gold(){
    this.block[1][4] = new Block();
}

In java class you can define variables or methods (including constructors) but can not use plain code in it.

Answer 6

You need to wrap your code in a method, not in the class body. If its part of the initialization of the Gold class put it inside its constructor like:

public class Gold {

    Block[][] block = new Block[4][4];

    public Gold() {
          this.block[1][4] = new Block();
    }

}

The class body allows only variable declaration and instantiations, but not standard operations like changing an object's (your array) value.

EDIT: as other pointed out, the index 4 does not exist in an array of size 4 , only indices from 0 to 3 can be accessed.

Answer 7

this.block[1][4] = new Block(); //1

is an expression not a field initialization. It cannot be outside of a method body.

Answer 8

This sentence

this.block[1][4] = new Block(); //1

cannot go outside a method or Initialisation block. If you want to initialize the array you have to do it on the declaration or inside a method (constructor could be a good place) or you have to use a Initialisation block.

Also check the array bounds. In Java arrays have 0 based indexes.

Answer 9

The code this.block[1][4] = new Block() is compiled but will fail on runtime: your array has 4 elements while index in java and all C-like languages starts from 0, so the max value of 4-elements long array is 3.

And you cannot write code outside methods in java, so if you try this you get compilation error.