GC of "new String()"

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September 25

Quited different between " " and new String(" "), if String contents are equal.

Test1:

Set<String> collection = new HashSet<String>();

String sql = null;

for ( int i=0; i<100000; i ++ ){

sql = "xyz";

collection .add(sql);

}

System.out.print("done. You can check the jvm");

Thread.sleep(10000);

num   #instances    #bytes class name
--------------------------------------
1:       523       87208 [C
2:       135       47920 [B
3:        12       31096 [I
4:       323       13824 [Ljava.lang.Object;
5:        32       10240 <objArrayKlassKlass>
6:       385        9240 java.lang.String
7:        92        4416 java.nio.HeapCharBuffer
8:        91        4368 java.nio.HeapByteBuffer
9:        42        4032 java.lang.Class
10:        55        3960 java.lang.reflect.Field
11:        56        1888 [Ljava.lang.String;
12:        11        1720 <constMethodKlass>
13:        45        1472 <symbolKlass>
14:        18        1440 [Ljava.util.HashMap$Entry;
15:        58        1392 java.util.Hashtable$Entry
16:        10        1040 [Ljava.util.Hashtable$Entry;
17:        61         976 java.lang.StringBuilder

Test 2:

Set<String> collection = new HashSet<String>();

String sql = null;

for ( int i=0; i<100000; i ++ ){

sql = new String( "xyz");

collection .add(sql);

}

System.out.print("done. You can check the jvm");

Thread.sleep(10000);

num   #instances    #bytes class name
--------------------------------------
1:     31782      762768 java.lang.String
2:       212       45528 [C
3:        17       25520 [B
4:        58       21632 [I
5:       312       13024 [Ljava.lang.Object;
6:        32       10240 <objArrayKlassKlass>
7:        42        4032 java.lang.Class
8:        47        3384 java.lang.reflect.Field
9:        11        1728 <constMethodKlass>
10:        48        1648 [Ljava.lang.String;
11:        45        1472 <symbolKlass>

8:33 PM | Blog it | 计算机与 Internet

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