VectorMath.java

// Only scalar values, both for parameters and return values.
// Calculation must be split into 2 methods. Ugly code, duplicate calculations.
public final class VectorMath {
	
	public static double getRotatedX(final double x, final double y,
			final double angle) {
		return x * Math.cos(angle) - y * Math.sin(angle);
	}


	public static double getRotatedY(final double x, final double y,
			final double angle) {
		return y * Math.cos(angle) + x * Math.sin(angle);

	}
}

VectorMath2.java

// Scalar values as parameters. Object as return value. 
// nicer code, no duplicate calculations
// But an extra allocation. Can java optimize this away?
public final class VectorMath2 {
	
	public static Vec2 getRotated(final double x, final double y,
			final double angle) {
		double cos = Math.cos(angle);
		double sin = Math.sin(angle);
		
		return new Vec2(x * cos - y * sin,  y * cos + x * sin);
	}

}

VectorMath3.java

// Scalar values for both parameters and return value. 
// Even nicer code, no duplicate calculations.
// But the caller needs to allocate an Vector object and another one is allocated for the return value.
// Can java optimize those allocations away?
public final class VectorMath {
	
	public static Vec2 getRotated(Vec2 p,
			final double angle) {
		double cos = Math.cos(angle);
		double sin = Math.sin(angle);
				
		return new Vec2(p.x * cos - p.y * sin,  p.y * cos + p.x * sin);
	}

}

VectorMath4.java

// Object as parameter, but no return value.
// Instead a second parameter in which the result is written.
// The caller can preallocate 2 Vec2 objects on startup. No allocations in the loop are needed.
// Code is a bit ugly because a parameter is used for the return value.
public final class VectorMath {
	
	public static void getRotatedInto(Vec2 p,
			final double angle, Vec2 target) {
		double cos = Math.cos(angle);
		double sin = Math.sin(angle);
				
		target.x = p.x * cos - p.y * sin;
		target.y = p.y * cos + p.x * sin;
	}

}