Improve Java code: too many if's

Question

I have several cases and I am just using simple if ... if else blocks.

How can I reduce the number of if statements in this code?

Perhaps I could use a lookup table, but I am not sure how to implement it in Java.

private int transition(char current, int state)
{
    if(state == 0)
    {
        if(current == 'b')
        {
            return 1;
        }
        else 
            return 0;
    }
    if(state == 1)
    {
        if(current == 'a')
        {
            return 2;
        }
        else 
            return 0;
    }
    if(state == 2)
    {
        if(current == 's')
        {
            return 3;
        }
        else 
            return 0;
    }
    if(state == 3)
    {
        if(current == 'e')
        {
            return 3;
        }
        if(current == 'b')
        {
            return 4;
        }
        else 
            return 0;
    }
    if(state == 4)
    {
        if(current == 'a')
        {
            return 5;
        }
        else 
            return 0;
    }
    if(state == 5)
    {
        if(current == 'l')
        {
            return 6;
        }
        else 
            return 0;
    }
    else
        return 0;
}

Answer 1

What you're trying to do looks very much like a finite state machine, and these are usually implemented with the help of a transition table. Once you set up the table, it's simply a matter of indexing to the position you want to get the return value. Assuming your return values are all less than 256, you can use a 2D byte array:

byte table[][] = new byte[NUM_STATES][NUM_CHARACTERS];
// Populate the non-zero entries of the table
table[0]['b'] = 1;
table[1]['a'] = 2;
// etc...

private int transition(char current, int state) {
  return table[state][current];
}