在OutOfMemoryError（Java）之前计算对象

Question

I'm a beginner in programming and I'm trying to compare different types of GC by running code below with 4 types of keys.

public class User {

    private String name;
    private int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    protected void finalize() throws Throwable {
        super.finalize();
        System.out.println("Finalized.");
    }

    public static void showInfo() {
        Runtime runtime = Runtime.getRuntime();
        System.out.println("##### Heap utilization statistics [bytes] #####");
        System.out.println("Used memory: " + (runtime.totalMemory() - runtime.freeMemory()) + " bytes");
        System.out.println("Free memory: " + runtime.freeMemory() + " bytes");
        System.out.println("Total memory: " + (runtime.totalMemory()) + " bytes");
        System.out.println("Max memory: " + (runtime.maxMemory()) + " bytes");
    }

    public static void main(String[] args) {
        int num = 0;
        System.out.println("Start...");
        for (int i = 0; i < 54000; i++) {
            num++;
            new User("Bob", 25);
        }
        System.out.println("Objects created before error: " + num);
        showInfo();
        System.out.println("Finish.");
    }
}

The keys are (each represents one of the GC type):

-XX:+UseSerialGC
-XX:+UseParallelOldGC
-XX:+UseParNewGC
-XX:+UseConcMarkSweepGC

And I'm using a small 3mb heap ( -Xmx3mb ).

So, the question is how to count number of created objects before OutOfMemoryError (before Java Heap Space error) ? I mean in that code the number of created objects is 54000, but if I'm trying to create more (70000, 80000, etc), I have an error and don't know after what number of object the exception is thrown. Is there a good way to count, how many objects we can create before OutOfMemoryError?

Answer 1

public static void main(String[] args) {
        int num = 0;
        System.out.println("Start...");
        for (int i = 0; i < 54000; i++) {
            try {
                new User("Bob", 25);
                num++;
            } catch(OutOfMemoryError e) {
                break;
            }
        }
        System.out.println("Objects created before error: " + num);
        showInfo();
        System.out.println("Finish.");
    }

You have to catch the exception and only increment the counter if the object is succefully created.