Skip to main content ☰ Contents Index You! < Prev ^ Up Next > \(\newcommand{\powerset}[1]{\mathcal{P}(#1)}
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\)
Section C.16 J1: Intro to Java
Synopsis.
Start with comparison of C and Java.
C
Java
struct
class
container
object
function
method
pointer
reference
malloc
new
free
garbage collection (no leaks, no dangling pointers)
unsigned
—
undefined behavior
—
sanitizer
totalized semantics
Outline basic compilation process. .java \(\to\) .class \(\to\) JVM
Overview over Types. Base types vs reference types.
Cannot take address of base type variables, cannot allocate them on the heap, lifetime determined by scopes.
No * and &.
Reference types are classes and arrays.
Allocated with new, life time governed by garbage collection.
A reference either contains “null” or references a live object.
Intro arrays.
Array contains elements and length.
You can query the length with “.length”.
Cannot increase the length, use “ArrayList” for array lists.
No multi-dimensional arrays.
String is a class that consists of character array.
First simple example: HelloWorld, compile manually with “javac” and run with JVM “java”.
Switch to IDE. Start with “Vec2” example. Use C program to motivate classes.
Proper way of encapsulation in C: Header file with anonymous struct, set of functions, first parameter is always ptr to struct that represents data structure.
In Java, you have more syntactic sugar. You can put functions/methods inside the class, “this” is implicit first parameter: reference to object of class.
Objects need to be constructed: Introduce constructors, default constructors.
Add main method and run example.
Add “Rectangle” class. How does it interact with “Vec2”? Encapsulate fields using getters and setter. Motivation: Can change internal implementation of “Vec2” to polar coordinates.
Show that setters are also a good means of asserting class invariants (Fraction example, setDenominator).
