为什么无限对象创建不会抛出OutOfMemoryError？

Question

Why am I not getting OutOfMemoryError with the below code?

class OutOfMemoryErrorTest{

    public static void main(String[] args){
        Object obj;

        while(true){
            obj = new Object();
        }
    }
}

I am running with Java 8.

Answer 1

The obj will be marked collectable after each loop, so it will be collected.

    while(true){
        Object obj = new Object(); //no further reference, so obj will be collected
    }

If you need to test OOM, you should save the reference of obj to a LinkedList.

    List refs = new LinkedList();
    while (true) {
        Object obj = new Object();
        refs.add(obj);
    }

Then you will get the OOM as you wanted. And you can use a smaller heap to reach OOM sooner.

Answer 2

Because you did not save the object reference, so garbage collector remove the created objects. if you add these objects to List then it will happened.

Answer 3

So firstly it simply gets removed by the garbage collector cause you create it in a loop. Secondly it could be you have so much memory that you just have to wait long. So when u fixed the garbage collector thing you may wait long. Try this code i found on https://crunchify.com/how-to-generate-out-of-memory-oom-in-java-programatically/

package test;

public class OutOfMemoryErrorTest {

    /**
     * @author Crunchify.com
     * @throws Exception
     * 
     */

    public static void main(String[] args) throws Exception {
        OutOfMemoryErrorTest memoryTest = new OutOfMemoryErrorTest();
        memoryTest.generateOOM();
    }

    public void generateOOM() throws Exception {
        int iteratorValue = 20;
        System.out.println("\n=================> OOM test started..\n");
        for (int outerIterator = 1; outerIterator < 20; outerIterator++) {
            System.out.println("Iteration " + outerIterator + " Free Mem: " + Runtime.getRuntime().freeMemory());
            int loop1 = 2;
            int[] memoryFillIntVar = new int[iteratorValue];
            // feel memoryFillIntVar array in loop..
            do {
                memoryFillIntVar[loop1] = 0;
                loop1--;
            } while (loop1 > 0);
            iteratorValue = iteratorValue * 5;
            System.out.println("\nRequired Memory for next loop: " + iteratorValue);
            Thread.sleep(1000);
        }
    }

}