new Integer(123) will create a new Object instance for each call.
According to the javadoc, Integer.valueOf(123) has the difference it caches Objects... so you may (or may not) end up with the same Object if you call it more than once.
For instance, the following code:
public static void main(String[] args) {
Integer a = new Integer(1);
Integer b = new Integer(1);
System.out.println("a==b? " + (a==b));
Integer c = Integer.valueOf(1);
Integer d = Integer.valueOf(1);
System.out.println("c==d? " + (c==d));
}
Has the following output:
a==b? false
c==d? true
As to using the int value, you are using the primitive type (considering your method also uses the primitive type on its signature) - it will use slightly less memory and might be faster, but you won't be ale to add it to collections, for instance.
Also take a look at Java's AutoBoxing if your method's signature uses Integer- when using it, the JVM will automatically call Integer.valueOf() for you (therefore using the cache aswell).
new Integer(123) will create a new Object instance for each call.
According to the javadoc, Integer.valueOf(123) has the difference it caches Objects... so you may (or may not) end up with the same Object if you call it more than once.
For instance, the following code:
public static void main(String[] args) {
Integer a = new Integer(1);
Integer b = new Integer(1);
System.out.println("a==b? " + (a==b));
Integer c = Integer.valueOf(1);
Integer d = Integer.valueOf(1);
System.out.println("c==d? " + (c==d));
}
Has the following output:
a==b? false
c==d? true
As to using the int value, you are using the primitive type (considering your method also uses the primitive type on its signature) - it will use slightly less memory and might be faster, but you won't be ale to add it to collections, for instance.
Also take a look at Java's AutoBoxing if your method's signature uses Integer- when using it, the JVM will automatically call Integer.valueOf() for you (therefore using the cache aswell).
public static Integer valueOf(int i)Returns a Integer instance representing the specified int value. If a new Integer instance is not required, this method should generally be used in preference to the constructor Integer(int), as this method is likely to yield significantly better space and time performance by caching frequently requested values.
Parameters:
i- an int value.
Returns:
aInteger instance representingi.
Since:
1.5
refer http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Integer.html#valueOf%28int%29
This variant of valueOf was added in JDK 5 to Byte, Short, Integer, and Long (it already existed in the trivial case in Boolean since JDK 1.4). All of these are, of course, immutable objects in Java. Used to be that if you needed an Integer object from an int, you’d construct a new Integer. But in JDK 5+, you should really use valueOf because Integer now caches Integer objects between -128 and 127 and can hand you back the same exact Integer(0) object every time instead of wasting an object construction on a brand new identical Integer object.
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);
}
}
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);
}
refer Why YOU should use Integer.valueOf(int)
EDIT
autoboxing and object creation:
The important point we must consider is that autoboxing doesn't reduce object creation, but it reduces code complexity. A good rule of thumb is to use primitive types where there is no need for objects, for two reasons:
Primitive types will not be slower than their corresponding wrapper types, and may be a lot faster. There can be some unexpected behavior involving == (compare references) and .equals() (compare values).
Normally, when the primitive types are boxed into the wrapper types, the JVM allocates memory and creates a new object. But for some special cases, the JVM reuses the same object.
The following is the list of primitives stored as immutable objects:
boolean values true and false
All byte values
short values between -128 and 127
int values between -128 and 127
char in the range \u0000 to \u007F
refer http://today.java.net/pub/a/today/2005/03/24/autoboxing.html#performance_issue
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I have to enter a text. I would have thought both were true. I meant to say 10 == new Integer(10)