autoboxing : Java Glossary

autoboxing

JDK 1.5 introduced a bit of syntactic sugar to save you writing conversions back and forth between Integer and int, Long and long, Double and double etc. If you leave out the conversion, the compiler will insert it for you. This provides the illusion that you can store primitive int, long, double etc. in Collections directly.

Converting from int to Integer is called boxing and converting back from Integer to int is called unboxing. In JDK 1.5+, both are automatic.

In code prior to JDK 1.1, you had to do a lot of manual tedious converting back and forth from primitive int to Integer Object, and similarly for byte/ Byte, char/Character, short/ Short, long/ Long, float/ Float and double/ Double.

In JDK 1.5+, these conversions are inserted for you automatically. You still pay the time penalty for the conversions, it is just you don’t have to spell them out longhand.

Autoboxing will interconvert Integer and int transparently, but not Integer[] and int[]. That you will have to do yourself element by element.

Manual Vs AutoBoxing	Learning More
AutoBoxing Example	Links
Manual Boxing Example

Manual Vs AutoBoxing

AutoBoxing Example

In this case we use a String to look up a number in a HashMap. We use the JDK 1.5+ autoboxing features and the JDK 1.5+ style for:each loop.

Old Style Manual Boxing Example

In this case we use a String to look up a number in a HashMap. We use the JDK 1.1+ manual boxing and the old style for loop. We don’t use generics type checking.

Learning More

Sun’s JDK Technote Guide on autoboxing : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 on your local Windows J: drive.

Autoboxing Conversion
Autoboxing Yourself
Autoboxing/Unboxing of Wrappers
conversion
conversion Amanuensis
HashMap
int vs Integer
JDK

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