Compressed Oops Example

Memory.java

public class Memory {

    // Dummy Entity representing usual data objects
    private static class Entity {
	public String name;
	public String detail;
	public Double amount;
	public Integer age;
    }

    // Linked list offers table inserts and helps illustrating the issue by using multiple
    // references per entry
    public static java.util.LinkedList<Entity> entities = new java.util.LinkedList<>();

    // This threshold should be 2 times Xmn. It ensures the loop stops before a full GC happens.
    private static final int MB = 1024 * 1024;
    private static final int THRESHOLD = 100 * MB;

    public static void main(String[] args) {
	System.out.println("Total Memory (in bytes): " + Runtime.getRuntime().totalMemory());
	System.out.println("Free Memory (in bytes): " + Runtime.getRuntime().freeMemory());
	System.out.println("Max Memory (in bytes): " + Runtime.getRuntime().maxMemory());

	while (true) {
	    appendEntitiesToDataStructure();
	    terminateBeforeFullGCorOOMEcanHappen();
	}
    }

    private static void appendEntitiesToDataStructure() {
	entities.add(new Entity());
    }

    private static void terminateBeforeFullGCorOOMEcanHappen() {
	if (Runtime.getRuntime().freeMemory() < THRESHOLD) {
	    System.out.println("Elements created and added to LinkedList: " + entities.size());
	    System.exit(0);
	}
    }

}