Java workaround for instanceof-CodePudding

I am making a GUI with function blocks in Java/Processing.

I have a general class which has methods just to manage the X and Y coordinates. All the blocks themselfs inherrit from the general class.

This allow me to make a single array list

ArrayList <FunctionBlock> blocks = new ArrayList() ;

I can add and remove function blocks at will.

The problem I am having is that I have to use instanceof. For instance.

    for (int i = 0; i < blocks.size(); i  )          // loop through all blocks
    {
        FunctionBlock block = blocks.get(i) ;        // declare a local function block

        if(block instanceof AND)    {    AND    and =   (AND) block ;   and.draw() ; }  // Can I do it differently?
        if(block instanceof OR)     {     OR     or =    (OR) block ;    or.draw() ; }
        if(block instanceof SR)     {     SR     sr =    (SR) block ;    sr.draw() ; }
        if(block instanceof DELAY)  {  DELAY  delay = (DELAY) block ; delay.draw() ; }
        if(block instanceof NOT)    {    NOT    not =   (NOT) block ;   not.draw() ; }
    }

Each individual function block has a draw() method. For every new block I add, I need to update this list among others.

I would prefer to use something like this

   for (int i = 0; i < blocks.size(); i  )          // loop through all blocks
    {
        FunctionBlock block = blocks.get(i) ;        // declare a local function block

         block.draw() ;    // compiler error ==> The function draw() does not exist.

In a single for-loop I want to call the draw() methods of all sub classes without having to check what the object is.

Is this possible and if so, how?

CodePudding user response：

The error is happening because the FunctionBlock has no method called draw(). Add this method to your class FunctionBlock class:

public abstract class FunctionBlock {
    /** Draws the block */
    public abstract void draw();
    ...

Then in your subclasses, add the @Override annotation to the implementations:

@Override
public void draw() {
    ...
}

Alternatively, you could define an interface that contains the draw method and then have your FunctionBlock class implement it:

interface Drawable {
    /** Draws the block */
    void draw();
}

public abstract class FunctionBlock implements Drawable {

If not every FunctionBlock class defines a draw() method, then you can have the individual subclasses implement the interface instead. If this is the case, you just have to change the type of block to Drawable