In the JDK 1.8 source code, why is A-B>0 used to determine which one is bigger instead of A>B?

Question content

As a beginner, I recently read the source code of jdk1.8. The question I'm having is why is a-b> 0 used to determine which is larger, rather than a> b?

The following code is in java/util/arraylist.java:236

private void ensureExplicitCapacity(int minCapacity) {
    modCount++;

    // overflow-conscious code
    if (minCapacity - elementData.length > 0)
        grow(minCapacity);
}

I can't understand the code for mincapacity - elementdata.length > 0. Why not use mincapacity > elementdata.length.

Correct answer

Probably to prevent mincapacity overflow, please check the following example:

public static void main(String[] args) {
    int elementDataLength = 10;
    int minCapacity = Integer.MAX_VALUE; // very big

    minCapacity += 1; // accidentally overflow it

    if (minCapacity > elementDataLength) {
        System.out.println("Will not work: minCapacity=-2147483647 elementDataLength=10");
    }
    if (minCapacity - elementDataLength > 0) {
        System.out.println("Will work: minCapacity - elementDataLength = 2147483638");
    }
}

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