Simple jump animation using Java/OpenGLES

Do I call a (Java)recursive function for a matrix oscillation (object moving back and forth) or rather nested if loops? Currently I've attempted as such:

public void Jump(double Strength, float[] mvpMatrix){
    	long time = SystemClock.uptimeMillis() % 4000L;
    	boolean Direction=true;
    	for(int u=0; u<2;u++){
	    	if (Direction==true){
		    	for (float i=0; i<Strength;i+=0.0001f){
		    		i=0.0001f*((int) time);
		    		Matrix.translateM(mvpMatrix, 0, i, 0.0f, 0.0f);
				draw(mvpMatrix);
				if (i>Strength)Direction=false;
		    	}
	    	}
	    	if (Direction==false){
		    	for (float i=Strength; i>0;i-=0.0001f){
		    		i=Strength-(0.0001f*((int) time));
		    		Matrix.translateM(mvpMatrix, 0, i, 0.0f, 0.0f);
				draw(mvpMatrix);
				if(u==2)return;
				if(i==0)Direction=true;
		    	}
	    	}
    	}
 }

But something seems to be wrong. The object moves in one direction and that's it. This function is located in the onDrawFrame() method.