找到了 public static Integer valueOf(String s) throws NumberFormatException { return new Integer(parseInt(s, 10)); } private static class IntegerCache { private IntegerCache(){} static final Integer cache[] = new Integer[-(-128) + 127 + 1]; static { for(int i = 0; i < cache.length; i++) cache[i] = new Integer(i - 128); } } /** * Returns a <tt>Integer</tt> instance representing the specified * <tt>int</tt> value. * If a new <tt>Integer</tt> 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. * * @param i an <code>int</code> value. * @return a <tt>Integer</tt> instance representing <tt>i</tt>. * @since 1.5 */ public static Integer valueOf(int i) { final int offset = 128; if (i >= -128 && i <= 127) { // must cache return IntegerCache.cache[i + offset]; } return new Integer(i); }
对于这样直接赋值的Integer 当值的范围在 [-128,127] 时候 会不生成新的对象 直接把缓存中的对对象拿来用 Integer a=128;Integer b=128这样的话就是false了可以看看Integer的源代码 里面有实现
{
return new Integer(parseInt(s, 10));
} private static class IntegerCache {
private IntegerCache(){} static final Integer cache[] = new Integer[-(-128) + 127 + 1]; static {
for(int i = 0; i < cache.length; i++)
cache[i] = new Integer(i - 128);
}
} /**
* Returns a <tt>Integer</tt> instance representing the specified
* <tt>int</tt> value.
* If a new <tt>Integer</tt> 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.
*
* @param i an <code>int</code> value.
* @return a <tt>Integer</tt> instance representing <tt>i</tt>.
* @since 1.5
*/
public static Integer valueOf(int i) {
final int offset = 128;
if (i >= -128 && i <= 127) { // must cache
return IntegerCache.cache[i + offset];
}
return new Integer(i);
}