Question

What is faster in Java. Accessing an array index directly multiple times, or saving the value of the array index to a new variable and use this for following compution?

acces index

if ((shape.vertices[0].x >= fromX && shape.vertices[0].x <= toX) || // left side of shape in screen
    (shape.vertices[0].x <= fromX && shape.vertices[0].x + shape.width >= fromX) || // right side of shape in screen
    (shape.vertices[0].x >= fromX && shape.vertices[0].x + shape.width <= toX)) { // shape fully in screen

    // ...
}

temp variable

float x = shape.vertices[0].x;
float y = shape.vertices[0].y;
if ((x >= fromX && x <= toX) || // left side of shape in screen
    (x <= fromX && x + shape.width >= fromX) || // right side of shape in screen
    (x >= fromX && x + shape.width <= toX)) { // shape fully in screen

        // ...
    }

Answer 1

The second approach is definitely faster. But you can help even more with the final keyword:

final float x = shape.vertices[0].x;
final float y = shape.vertices[0].y;
final int rightEdge = x + shape.width;
if ((x >= fromX && x <= toX) || // left side of shape in screen
(x <= fromX && rightEdge >= fromX) || // right side of shape in screen
(x >= fromX && rightEdge <= toX)) { // shape fully in screen

    // ...
}

Not a significant improvement of course (but still an improvement and also makes the intent clear). You can read this discussion: http://old.nabble.com/Making-copy-of-a-reference-to-ReentrantLock-tt30730392.html#a30733348