Shulou(Shulou.com)06/03 Report--

This article gives you an example of the caching mechanism of the Java wrapper class, which is very detailed. Interested friends can use it for reference. I hope it will be helpful to you.

The caching mechanism of the java wrapper class is a feature introduced in Java 5 to help save memory and improve performance, which is effective only when boxing automatically.

Integer wrapper class

Take a chestnut:

Integer a = 127 th Integer b = 127 th System.out.println (a = = b)

The output of this code is true

The underlying implementation of using autoboxing to convert a primitive type to a wrapper class object is to call the wrapper class's valueOf method:

Integer a = 127; equivalent to Integer a = Integer.valueOf

Take a look at Integer's valueOf method:

Public static Integer valueOf (int I) {if (I > = IntegerCache.low & & I = 127;} private IntegerCache () {}}

The default range is between-128and 127. the maximum value of the range can be set through java.lang.Integer.IntegerCache.high, and the data within the range can be instantiated into Integer objects and placed in the cache array through the for loop.

Take a test again:

Integer a = 128 th Integer b = 128 th System.out.println (a = = b)

The output is false, so if no cache maximum is specified, the cache will be used when autoboxing is used between-128and 127,

Byte wrapper class

Give me another chestnut:

Public static void main (String [] args) {Byte a = 127; Byte b = 127; System.out.println (a = = b); / / true}

Since the Byte ranges from-128to 127, the valueOf of Byte is obtained from the ByteCache cache.

Public static Byte valueOf (byte b) {final int offset = 128; return ByteCache.cache [(int) b + offset];}

ByteCache class:

Private static class ByteCache {private ByteCache () {} static final Byte cache [] = new Byte [- (- 128) + 127 + 1]; static {for (int I = 0; I)

=-128 & & sAsInt

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