Java Notes

Autoboxing

Autoboxing, introduced in Java 5, is the automatic conversion the Java compiler makes between the primitive (basic) types and their corresponding object wrapper classes (eg, int and Integer, double and Double, etc). The underlying code that is generated is the same, but autoboxing provides a sugar coating that avoids the tedious and hard-to-read casting typically required by Java Collections, which can not be used with primitive types.

Example

int i;
Integer j;
i = 1;
j = 2;
i = j;
j = i;

int i;
Integer j;
i = 1;
j = new Integer(2);
i = j.valueOf();
j = new Integer(i);

Prefer primitive types

Use the primitive types where there is no need for objects for two reasons.

1. Primitive types may be a lot faster than the corresponding wrapper types, and are never slower.
2. The immutability (can't be changed after creation) of the wrapper types may make it their use impossible.
3. There can be some unexepected behavior involving == (compare references) and .equals() (compare values). See the reference below for examples.

References

• Autoboxing surprises from J2SE 5 (www.theserverside.com/news/thread.tss?thread_id=27129) shows some problem areas with autoboxing.