是否确实有必要在JUnit拆卸方法中取消对象?[复制品]

我被 answer 类似的问题。我认为这是错误的。所以我创建了一些测试代码。我的问题是,这段代码是否证明/否定/不确定在拆卸方法中消除成员变量是有用的假设?我用JUnit4.8.1测试过。

JUnit为4个测试中的每一个创建一个新的测试类实例。每个实例都包含一个对象obj。该对象也作为静态weakhashmap的键插入。如果JUnit释放对测试实例的引用,则关联的obj值将变为弱引用,从而符合GC。测试试图强制GC。weakhashmap的大小将告诉我obj是否已被gc'ed。一些测试使obj变量无效,而其他测试则没有。

import org . junit . Before ;
import org . junit . After ;
import org . junit . Test ;
import java . util . ArrayList ;
import java . util . WeakHashMap ;
import java . util . concurrent . atomic . AtomicInteger ;
import static org . junit . Assert . * ;

public class Memory
{
    static AtomicInteger idx = new AtomicInteger ( 0 ) ;

    static WeakHashMap < Object , Object > map = new WeakHashMap < Object , Object > ( ) ;

    int id ;

    Object obj ;

    boolean nullify ;

    public Memory ( )
    {
    super ( ) ;
    }

    @ Before
    public void before ( )
    {
    id = idx . getAndIncrement ( ) ;
    obj = new Object ( ) ;
    map . put ( obj , new Object ( ) ) ;
    System . out . println ( "<BEFORE TEST " + id + ">" ) ;
    }

    void test ( boolean n )
    {
    nullify = n ;
    int before = map . size ( ) ;
    gc ( ) ;
    int after = map . size ( ) ;
    System . out . println ( "BEFORE=" + before + "\tAFTER=" + after ) ;
    }

    @ Test
    public void test0 ( )
    {
    test ( true ) ;
    }

    @ Test
    public void test1 ( )
    {
    test ( false ) ;
    }

    @ Test
    public void test2 ( )
    {
    test ( true ) ;
    }

    @ Test
    public void test3 ( )
    {
    test ( false ) ;
    }

    @ After
    public void after ( )
    {
    if ( nullify )
        {
        System . out . println ( "Nullifying obj" ) ;
        obj = null ;
        }
    System . out . println ( "<AFTER TEST " + id + ">" ) ;
    }

    /**
     * Try to force a gc when one is not really needed.
     **/
    void gc ( )
    {
    ArrayList < Object > waste = new ArrayList < Object > ( ) ;
    System . gc ( ) ; // only a suggestion but I'll try to force it
    list :
    while ( true ) // try to force a gc
        {
        try
            {
            waste . add ( new Object ( ) ) ;
            }
        catch ( OutOfMemoryError cause )
            {
            // gc forced? should have been
            waste = null ;
            break list ;
            }
        }
    System . gc ( ) ; // only a suggestion but I tried to force it
    }
}

我使用命令行界面运行了代码(使用-xmx128k选项来增加垃圾收集),得到了以下结果

.<BEFORE TEST 0>
BEFORE=1    AFTER=1
Nullifying obj
<AFTER TEST 0>
.<BEFORE TEST 1>
BEFORE=2    AFTER=1
<AFTER TEST 1>
.<BEFORE TEST 2>
BEFORE=2    AFTER=1
Nullifying obj
<AFTER TEST 2>
.<BEFORE TEST 3>
BEFORE=2    AFTER=1
<AFTER TEST 3>

test0 obj无效,在test1中是gc'ed。但是test1 obj没有无效,在test2中是gc'ed。这意味着不需要取消对象的无效性。