MemoryOccupyTest

MemoryOccupyTest

import org.junit.Test;

import java.util.ArrayList;
import java.util.List;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

/**
 * Created by zhuguowei on 4/12/17.
 */
public class MemoryOccupyTest {
    @Test
    public void test_add_diff_object() throws Exception {
        final Runtime runtime = Runtime.getRuntime();
        runtime.gc();
        Thread.sleep(1000);

        final long startMem = runtime.totalMemory() - runtime.freeMemory();

        List<Foo> fooList = new ArrayList<>(3);
        fooList.add(new Foo());
        fooList.add(new Foo());
        fooList.add(new Foo());

        final long endMem = runtime.totalMemory() - runtime.freeMemory();
        long diff = endMem - startMem;
        System.out.printf("start: %d end: %d diff: %d",startMem,endMem, diff);
        assertTrue(diff > 3*1024*1024);
    }
    @Test
    public void test_add_same_object() throws Exception {
        final Runtime runtime = Runtime.getRuntime();
        runtime.gc();
        Thread.sleep(1000);

        final long startMem = runtime.totalMemory() - runtime.freeMemory();

        List<Foo> fooList = new ArrayList<>(3);
        Foo foo = new Foo();
        fooList.add(foo);
        fooList.add(foo);
        fooList.add(foo);

        assertEquals(3, fooList.size());

        final long endMem = runtime.totalMemory() - runtime.freeMemory();
        long diff = endMem - startMem;
        System.out.printf("start: %d end: %d diff: %d",startMem,endMem, diff);
        assertTrue(diff < 2*1024*1024);
    }

    static class Foo{
        byte[] padding = new byte[1 * 1024 * 1024];
    }
}