public class IntegerTest03 {
private static void changeInteger(Integer value) {
value = Integer.valueOf(value.intValue() + 1);
}
public static void main(String[] args) {
Integer a = Integer.valueOf(1);
changeInteger(a);
}
}
查看 Integer 源码，可知valueOf()会将形参指向不同的 Integer 对象实例。
/**
* 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) {
assert IntegerCache.high >= 127;
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 -XX:AutoBoxCacheMax= 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) {
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);
}
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() {}
}
2.2 关于 IntegerCache
IntegerCache 在首次使用时被初始化，最小值为 -128，最大值默认为 127，也可以通过 VM 参数-XX:AutoBoxCacheMax=设置最大值。
@Test
public void test01() {
Integer a = 1;
Integer b = 1;
System.out.println(a == b);
Integer aa = 128;
Integer bb = 128;
System.out.println(aa == bb);
}
/**
* Created by Sumkor on 2018/9/10.
*/
public class StrongReferenceTest {
public static void main(String[] args) {
byte[] allocation01 = new byte[1024 * 1024 * 9];
byte[] allocation02 = new byte[1024 * 1024 * 9];
}
}
摘要：引用数据类型指针存放在局部变量表中，调用方法的时候，副本引用压栈，赋值仅改变副本的引用。方法执行完毕，不再局部变量不再被使用到，等待被回收。
小方法大门道
小瓜瓜作为一个Java初学者，今天跟我说她想通过一个Java方法，将外部变量通过参数传递到方法中去，进行逻辑处理，方法执行完毕之后，再对修改过的变量进行判断处理，代码如下所示。
public class MethodParamsPa...
