Quick C vs Java Refresher

Thing	C	Java
type of language	function oriented	object oriented
basic programming unit	function	class = ADT
portability of source code	possible with discipline	yes
portability of compiled code	no, recompile for each architecture	yes, bytecode is "write once, run anywhere"
security	limited	built-in to language
compilation	gcc hello.c creates machine language code	javac Hello.java creates Java virtual machine language bytecode
linking in the Math library	gcc -lm calculate.c	no special flags needed
joint compilation	gcc main.c helper1.c helper2.c	javac Main.java - any dependent files are automatically re-compiled if needed
execution	a.out loads and executes program	java Hello interprets byte code
hello, world	#include<stdio.h> int main(void) {    printf("Hello\n");    return 0; }	public class HelloWorld {    public static void main(String[] args) {        System.out.println("Hello");    } }
integer types	int usually 32 bit 2's complement; long usually 32 bit 2's complement	int is 32 bit 2's complement; long is 64 bit 2's complement
floating point types	float usually 32 bit; double usually 64 bit	float is 32 bit IEEE 754 binary floating point; double is 64 bit IEEE 754
boolean type	use int: 0 for false, nonzero for true	boolean is its own type - stores value true or false
character type	char is usually 8 bit ASCII	char is 16 bit UNICODE
for loops	for (i = 0; i < N; i++)	for (int i = 0; i < N; i++)
array declarations	int *a = malloc(N * sizeof(*a));	int[] a = new int[N];
array size	arrays don't know their own size	a.length
strings	'\0'-terminated character array	built-in immutable String data type
accessing a library	#include <stdio.h>	import java.io.File;
accessing a library function	#include "math.h" x = sqrt(2.2); all function and variables names are global	x = Math.sqrt(2.2); functions have different namespaces
printing to standard output	printf("sum = %d", x);	System.out.println("sum = " + x);
formatted printing	printf("avg = %3.2f", avg);	System.out.printf("avg = %3.2f", avg)
reading from stdin	scanf("%d", &x);	Java library support, but easier to use our library int x = StdIn.readInt();
memory address	pointer	reference
manipulating pointers	*, &, +	no direct manipulation permitted
functions	int max(int a, int b)	public static int max(int a, int b)
pass-by-value	primitive data types, structs, and pointers are passed by value; array decays to pointer	all primitive data types and references (which includes arrays), are passed by value
defining a data structure	struct	class - key difference is language support for defining methods to manipulate data
accessing a data structure	a.numerator for elements	a.numerator for instance variables, c = a.plus(b) for methods
pointer chasing	x->left->right	x.left.right
allocating memory	malloc	new
de-allocating memory	free	automatic garbage collection
memory allocation of data structures and arrays	heap, stack, data, or bss	heap
buffer overflow	segmentation fault, core dump, unpredicatable program	checked run-time error exception
declaring constants	const and #define	final
variable auto-initialization	not guaranteed	instance variables (and array elements) initialized to 0, null, or false, compile-time error to access uninitialized variables
data hiding	opaque pointers and static	private
interface method	non-static function	public method
data type for generic item	void *	Object
casting	anything goes	checked exception at run-time or compile-time
demotions	automatic, but might lose precision	must explicitly cast, e.g., to convert from long to int
polymorphism	union	inheritence
overloading	no	yes for methods, no for operators
graphics	use external libraries	Java library support, use our standard drawing library
null	NULL	null
enumeration	enum	typesafe enum
preprocessor	yes	no
variable declaration	at beginning of a block	before you use it
variable naming conventions	sum_of_squares	sumOfSquares
commenting	/* */	/* */ or //
file naming conventions	stack.c, stack.h	Stack.java - file name matches name of class
callbacks	pointers to global functions	use interfaces for commmand dispatching
variable number of arguments	varargs	String ...
assertions	assert	assert
exit and return value to OS	exit(1)	System.exit(1)