<分区>
Possible Duplicate:
Why does 128==128 return false but 127==127 return true in this code?
下面这段Java代码返回true
Integer i1=1;
Integer i2=1;
System.out.println(i1==i2);
那么我们在 Java 中有字符串常量池的概念，我们在 Java 中的包装类的情况下是否也有类似的概念？
<分区>
Possible Duplicate:
Why does 128==128 return false but 127==127 return true in this code?
下面这段Java代码返回true
Integer i1=1;
Integer i2=1;
System.out.println(i1==i2);
那么我们在 Java 中有字符串常量池的概念，我们在 Java 中的包装类的情况下是否也有类似的概念？
最佳答案
Java 也有用于 -128 到 127 之间的小整数的整数池，因此它对整数的行为与字符串常量池相似
您将在Integer 类中找到以下代码
private static class IntegerCache {
static final int high;
static final Integer cache[];
static {
final int low = -128;
// high value may be configured by property
int h = 127;
if (integerCacheHighPropValue != null) {
// Use Long.decode here to avoid invoking methods that
// require Integer's autoboxing cache to be initialized
int i = Long.decode(integerCacheHighPropValue).intValue();
i = Math.max(i, 127);
// Maximum array size is Integer.MAX_VALUE
h = Math.min(i, Integer.MAX_VALUE - -low);
}
high = h;
cache = new Integer[(high - low) + 1];
int j = low;
for(int k = 0; k < cache.length; k++)
cache[k] = new Integer(j++);
}
private IntegerCache() {}
}
也如以下毒药回答所述:
Chapter 5. Conversions and Promotions
if the value p being boxed is true, false, a byte, or a char in the range \u0000 to \u007f, or an int or short number between -128 and 127 (inclusive), then let r1 and r2 be the results of any two boxing conversions of p. It is always the case that r1 == r2.
关于java - Java 中 Wrapper 类的行为，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/12306853/