對於這些比較,記住只要是new的就在堆中,堆中就不一樣;
而直接賦值的數,都是在方法常量池中;
項目啓動時,java的IntegerCache會對於 -128到127之間的數進行緩存;
public static void main(String[] args){
int int1 = 1;
Integer int2 = 1;
Integer int3 = 1;
System.out.println(int1==int2); // true
System.out.println(int2==int3); // true
Integer int4 = new Integer(1);
Integer int5 = new Integer(1);
System.out.println(int3==int4); // false
System.out.println(int5==int4); // false
}
第一個爲true,是因爲Integer在比較前自動拆箱爲int,所以爲true
public static void main(String[] args){
int int1 = 1000;
Integer int2 = 1000;
Integer int3 = 1000;
System.out.println(int1==int2); // true
System.out.println(int2==int3); // false
Integer int4 = new Integer(1000);
Integer int5 = new Integer(1000);
System.out.println(int3==int4); // false
System.out.println(int5==int4); // false
}
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() {}
}
對於第二個爲false,是因爲int3 = 1000;大於127了,需要重新new,所以不一樣