So, I'm not sure what the situation is with Java, but I suspect there might be some confusion in what you're reading. In C#, anything instantiated as part of a

So, I'm not sure what the situation is with Java, but I suspect there might be some confusion in what you're reading. In C#, anything instantiated as part of a class goes onto the heap. Value types that are declared and used only within the function are allocated onto the stack. For example: public class Example { public int a; // Allocated onto the heap when Example is instanced public int b; // Allocated onto the heap when Example is instanced public int c; // Allocated onto the heap when Example is instanced public void CycleValues() { int temp = a; // Allocated onto the stack when function is called a = b; // a, b, and c are already allocated b = c; c = temp; // temp goes away when the function finishes executing } public int SumPositiveValues() { List<int> positiveList = new List(); // Not a value type: allocates onto the heap if (a > 0) valueList.Add(a); if (b > 0) valueList.Add(b); if (c > 0) valueList.Add(c); int sum = 0; // Allocated onto the stack foreach (int i in valueList) { sum += i; } return sum; // sum goes away when the function finishes executing // positiveList was allocated onto the heap, so it persists (although inaccessible) until garbage collection } } In the example above, space on the heap is allocated when you create a new Example(). Calling CycleValues() doesn't allocate anything new onto the heap, so it isn't creating any garbage. Calling SumPositiveValues() creates a new List(), which, not being a value type, is allocated onto the heap. When the function finishes, that memory isn't automatically freed; it creates garbage. Optimising for heap performance relies a lot on removing New calls to classes when it is possible and makes sense to do so.