Integer tmp = new Integer(10);
Integer tmp1 = Integer.valueOf(1);
new Integer
构建一个新分配的对象,该对象代表指定的值。
解析: 相当于在堆中创建了一个新的对象来代表这个值。
/**
* Constructs a newly allocated {@code Integer} object that
* represents the specified {@code int} value.
*
* @param value the value to be represented by the
* {@code Integer} object.
*/
public Integer(int value) {
this.value = value;
}
Integer.valueOf
首先判断这个值是否在-128到127之间;如果不在,则new 一个Integer,反之,在我们第一次使用IntegerCache.cache[i + (-IntegerCache.low)]的时候;会初始化IntegerCache类,加载静态常量cache[], 静态方法块;静态方法块中默认创建了代表-128-127值的对象放在cache数组中。
注意:IntegerCache是静态内部类,是懒加载模式,只有在第一次被调用时才会去加载到方法区中会。
优点:缓存频繁被请求的值,产生更好的空间和时间性能。
/**
* Returns an {@code Integer} instance representing the specified
* {@code int} value. If a new {@code Integer} instance is not
* required, this method should generally be used in preference to
* the constructor {@link #Integer(int)}, as this method is likely
* to yield significantly better space and time performance by
* caching frequently requested values.
*
* This method will always cache values in the range -128 to 127,
* inclusive, and may cache other values outside of this range.
*
* @param i an {@code int} value.
* @return an {@code Integer} instance representing {@code i}.
* @since 1.5
*/
public static Integer valueOf(int i) {
if (i >= IntegerCache.low && i <= IntegerCache.high)
return IntegerCache.cache[i + (-IntegerCache.low)];
return new Integer(i);
}
/**
* Cache to support the object identity semantics of autoboxing for values between
* -128 and 127 (inclusive) as required by JLS.
*
* The cache is initialized on first usage. The size of the cache
* may be controlled by the {@code -XX:AutoBoxCacheMax=<size>} option.
* During VM initialization, java.lang.Integer.IntegerCache.high property
* may be set and saved in the private system properties in the
* sun.misc.VM class.
*/
private static class IntegerCache {
static final int low = -128;
static final int high;
static final Integer cache[];
static {
// high value may be configured by property
int h = 127;
String integerCacheHighPropValue =
sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
if (integerCacheHighPropValue != null) {
try {
int i = parseInt(integerCacheHighPropValue);
i = Math.max(i, 127);
// Maximum array size is Integer.MAX_VALUE
h = Math.min(i, Integer.MAX_VALUE - (-low) -1);
} catch( NumberFormatException nfe) {
// If the property cannot be parsed into an int, ignore it.
}
}
high = h;
cache = new Integer[(high - low) + 1];
int j = low;
for(int k = 0; k < cache.length; k++)
cache[k] = new Integer(j++);
// range [-128, 127] must be interned (JLS7 5.1.7)
assert IntegerCache.high >= 127;
}
private IntegerCache() {}
}