三元声明突围而出

Question

I am writing a vertices class for an android project within Eclipse and within the constructor I am having a run-time bug. Here is the constructor...

public Vertices(GLGraphics glGraphics, int maxVertices, int maxIndices, boolean hasColor, boolean hasTexCoords)
{
    this.glGraphics = glGraphics;
    this.hasColor = hasColor;
    this.hasTexCoords = hasTexCoords;
    this.vertexSize = (2 + (hasColor?4:0) + (hasTexCoords?2:0)) * 4;

    ByteBuffer buffer = ByteBuffer.allocateDirect(maxVertices * vertexSize);
    buffer.order(ByteOrder.nativeOrder());
    vertices = buffer.asFloatBuffer();

    if(maxIndices > 0)
    {
        buffer = ByteBuffer.allocateDirect(maxIndices * Short.SIZE / 8);
        buffer.order(ByteOrder.nativeOrder());
        indices = buffer.asShortBuffer();
    }
    else
    {
        indices = null;
    }
}

In this statement:

this.vertexSize = (2 + (hasColor?4:0) + (hasTexCoords?2:0)) * 4;

I am calculating the size of the vertex in bytes. The problem is that whenever a ternary operation is evaluated, vertexSize remains at 0 and the program breaks out of the constructor at that statement. The ternary operator is not evaluating to it's value depending on whether the condition is true or false. What is going on here?

Answer 1

You're experiencing a Null Pointer Exception. The first operand of the ternary operator cannot be null .

When you run this line, hasColor must be coming in as null, causing your program to give you a run time error. This will cause your program to end and vertexSize will never be assigned.

this.vertexSize = (2 + (hasColor?4:0) + (hasTexCoords?2:0)) * 4;

Check your logcat, it should show you that this is the case.

EDIT

As @jahroy mentioned, although it would throw an NPE at this line, its probably actually throwing the NPE when its passed into the constructor. If you attempt to cast null to a boolean, you will also get an NPE.

Answer 2

Part of the problem is that you are trying to do too much in a single line of code. I strongly suggest that you break

this.vertexSize = (2 + (hasColor?4:0) + (hasTexCoords?2:0)) * 4;

Into about three lines of code:

int colorWeight = hasColor ? 4 : 0;
int texCoordWeight = hasTexCoords ? 2 : 0;

this vertexSize = (2 + colorWeight + texCoordWeight) * 4

Notice how much easier this is to read. Also, when you get error messages, it is much easier to track down the cause.