slides

Foundations of Programming Languages
Boxing and Unboxing
Prof. Dr. Christoph Reichenbach
Fachbereich 12 / Institut für Informatik
14. November 2014
Boxing
I
I
Strings, lists etc. as objects on the heap
int? double?
Separation Objects / Primitive Types Universal Objects
(Python, Haskell (partly))
(AttoVM, Java)
int i = 0;
Object o = new Object ();
Advantages:
I
Higher performance during
arithmetic
I
I
Everything is an object
Built-in ops for arithmetic
Advantages:
I
I
Simple semantics
Simple implementation
2/4
Automatic Boxing and Unboxing
Example Java (LinkedList):
LinkedList<Integer> ll = new LinkedList<>();
1 );
ll.add(
int i = ll.get(0)
+ 3;
3/4
Automatic Boxing and Unboxing
Example Java (LinkedList):
LinkedList<Integer> ll = new LinkedList<>();
ll.add(new Integer(1));
int i = ll.get(0).intValue() + 3;
3/4
Summary
I
I
I
I
Some languages distinguish between boxed and unboxed
values
Boxed: primitive value is packed into heap object
Unboxed: primitive value is stored as literal value
Boxing/Unboxing: conversion between the two
4/4