CODEWITHSUNDEEP
javamemory-managementmemory-leaksout-of-memory
pjj
pjj

Reputation: 2135

Obsolete reference and out of memory error

Why version4 method throws out of memory error but version3 method doesn't throw it, I think in both the cases there is problem is "obsolete reference"?

private static void version4() {
    int count = 0;
    long start = System.nanoTime();
    try {
        List<Calendar> list = new ArrayList<>();
        System.out.println(list.size());
        while(true){
            for (int i = 0; i < 1000; i++) {
                Calendar calendar = Calendar.getInstance();
                list.add(i, calendar);
            }
        }
    } catch (Error e) {
        e.printStackTrace();
    }
    long end = System.nanoTime();
    System.out.println("count: " + count + " | time:" + (end - start)/1000000);
}

private static void version3() {
    int count = 0;
    long start = System.nanoTime();
    try {
        Calendar[] calendars = new Calendar[1000]; 
        while(true){
            for (int i = 0; i < calendars.length; i++) {
                Calendar calendar = Calendar.getInstance();
                calendars[i] = calendar;
            }
        }
    } catch (Error e) {
        e.printStackTrace();
    }
    long end = System.nanoTime();
    System.out.println("count: " + count + " | time:" + (end - start)/1000000);
}

Upvotes: 0

Views: 115

Answers (1)

davidxxx
davidxxx

Reputation: 131346

In both cases you loop forever because of the outer while (true).
But in the array case, in the inner loop you overwrite old values of the array (that has a length of 1000). So the memory consumption is about constant.
While in the ArrayList case you add new Calendar objects in the inner loop. So the memory usage grows constantly : 1000 (first loop) + 1000 (second loop) + ...

Upvotes: 3

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