GLThread java.lang.NullPointerException error

Question

I developing opengl android app using opengl ES 2.0. My app crashes and write in log this:

07-28 22:55:29.460 13407-13420/?
E/AndroidRuntime: FATAL EXCEPTION: GLThread 1293 java.lang.NullPointerException at com.jayway.gles20.GLES20Renderer.draw_worlddate(GLES20Renderer.java:521) at com.jayway.gles20.GLES20Renderer.onDrawFrame(GLES20Renderer.java:503) at com.jayway.gles20.GLRenderer.onDrawFrame(GLRenderer.java:87) at android.opengl.GLSurfaceView$GLThread.guardedRun(GLSurfaceView.java:1516) at android.opengl.GLSurfaceView$GLThread.run(GLSurfaceView.java:1240)

Error in this function:

public void draw_worlddate(String wtype){
    Map<String,float[][][]> wdw=worlddate.world;
    float[][][] ww;
    ww = wdw.get(wtype);
    float[][] ww2;
    float[] ww3;
    for (int i=0;i<ww.length;i++){//this is line 521
        ww2=ww[i];

        Matrix.setIdentityM(mModelMatrix, 0);
        for(Integer i2=0;i2<ww2.length;i2++){

            ww3=ww2[i2];
            switch (i2){
                case 0:
                    Matrix.translateM(mModelMatrix,0,ww3[0],ww3[1],ww3[2]);
                break;
                case 1:
                    Matrix.rotateM(mModelMatrix,0,0.0f,ww3[0],ww3[1],ww3[2]);
                break;
                case 2:
                    Matrix.scaleM(mModelMatrix,0,ww3[0],ww3[1],ww3[2]);
                break;
            }
        }
        drawTriangle(mTriangle1Vertices);
    }
}

The parsing array int the Map:

 {
            {
                    {
                            1.0f,
                            1.0f,
                            1.0f
                    },
                    {
                            1.0f,
                            1.0f,
                            1.0f
                    },
                    { 
                            1.0f,
                            1.0f,
                            1.0f
                    }
            }
    }

How to fix this?

Answer 1

Check that the Map wdw contains a value for the associated key before attempting to determine the length of the retrieved array

if (wdw.containsKey(wtype)) {
   ww = wdw.get(wtype);
   ...
   for (int i=0; i <ww.length;i++){
     ...
   }
}