Integer缓存机制-基本数据类型和包装类型-自动拆…

public static Integer valueOf(int i) {
        if (i >= IntegerCache.low && i <= IntegerCache.high)
            return IntegerCache.cache[i + (-IntegerCache.low)];
        return new Integer(i);
    }

 1 /**
 2      * Cache to support the object identity semantics of autoboxing for values between
 3      * -128 and 127 (inclusive) as required by JLS.
 4      *
 5      * The cache is initialized on first usage.  The size of the cache 第一次使用时生效
 6      * may be controlled by the {@code -XX:AutoBoxCacheMax=<size>} option. 可通过参数设置最大值
 7      * During VM initialization, java.lang.Integer.IntegerCache.high property
 8      * may be set and saved in the private system properties in the
 9      * sun.misc.VM class.
10      */
11 
12     private static class IntegerCache {
13         static final int low = -128;
14         static final int high;
15         static final Integer cache[];
16 
17         static {
18             // high value may be configured by property
19             int h = 127;
20             String integerCacheHighPropValue =
21                 sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
22             if (integerCacheHighPropValue != null) {
23                 try {
24                     int i = parseInt(integerCacheHighPropValue);
25                     i = Math.max(i, 127);
26                     // Maximum array size is Integer.MAX_VALUE
27                     h = Math.min(i, Integer.MAX_VALUE - (-low) -1);
28                 } catch( NumberFormatException nfe) {
29                     // If the property cannot be parsed into an int, ignore it.
30                 }
31             }
32             high = h;
33 
34             cache = new Integer[(high - low) + 1];
35             int j = low;
36             for(int k = 0; k < cache.length; k++)
37                 cache[k] = new Integer(j++);
38 
39             // range [-128, 127] must be interned (JLS7 5.1.7)
40             assert IntegerCache.high >= 127;
41         }
42 
43         private IntegerCache() {}
44     }

 1 private static class IntegerCache {
 2         static final Integer[] cache = new Integer[256];
 3 
 4         static {
 5             for (int i = 0; i < cache.length; i++) {
 6                 cache[i] = new Integer(i - 128);
 7             }
 8         }
 9     }
10 
11     public static Integer valueOf(int paramInt) {
12         if ((paramInt >= -128) && (paramInt <= 127)) {
13             return IntegerCache.cache[(paramInt + 128)];
14         }
15         return new Integer(paramInt);
16     }

1 Integer i = 1;
2 int j = i;
3 
4 /**
5 *    上面代码编译成class后
6 */
7 Integer i = Integer.valueOf(1);
8 int j = i.intValue();