This page provides a quick comparison of C to Java Programming.

Areas of Comparison

 

Sample Program Comparison

C Programming

helloworld.c

#include<stdio.h>
int main(void) {
    printf("Hello\n");
    return 0;
}

Java Programming

HelloWorld.java

public class HelloWorld {
   public static void main(String[] args) {
       System.out.println("Hello");
   }
}

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General Comparisons

Language Type

C Programming

function oriented

Java Programming

object oriented

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Basic Programming Unit

C Programming

function

Java Programming

class

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Portability of Source Code

C Programming

possible with discipline

Java Programming

yes

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Portability of Compiled Code

C Programming

no, recompile for each architecture

Java Programming

yes, bytecode is “Write once, run anywhere” (WORA)

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Security

C Programming

limited

Java Programming

built-in to language

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Compilation

C Programming

creates machine language code

gcc hello.c

Java Programming

creates Java virtual machine language bytecode

javac Hello.java

Linking in the Math Library

C Programming

gcc -lm calculate.c

Java Programming

no special flags needed

Joint Compilation

C Programming

gcc main.c helper1.c helper2.c

Java Programming

any dependent files are automatically re-compiled if needed

javac Main.java

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Execution

C Programming

a.out

loads and executes program

Java Programming

java Hello

interprets byte code

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memory Address

C Programming

pointer

Java Programming

reference

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Data Type Comparisons

Primitive Integer Types

C Programming

int

usually 32 bit 2’s complement

Java Programming

int

is 32 bit 2’s complement

Primitive Long Types

C Programming

long

usually 32 bit 2’s complement

Java Programming

long

is 64 bit 2’s complement

Primitive Float Types

C Programming

float

usually 32 bit

Java Programming

float

is 32 bit IEEE 754 binary floating point

Primitive Double Types

C Programming

double

usually 64 bit

Java Programming

double

is 64 bit IEEE 754

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Primitive Boolean Types

C Programming

int

uses 0 for false, nonzero for true

Java Programming

boolean

is its own type – stores value 

true

or 

false

Primitive Character Types

C Programming

char

is usually 8 bit ASCII

Java Programming

char

is 16 bit UNICODE

Primitive Character Types

C Programming

char

is usually 8 bit ASCII

Java Programming

char

is 16 bit UNICODE

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For Loops

C Programming

for (i = 0; i < N; i++)

Java Programming

for (int i = 0; i < N; i++)

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Arrays

Array Declarations

C Programming

int *a = malloc(N * sizeof(*a));

Java Programming

int[] a = new int[N];

Array Size

C Programming

arrays don’t know their own size

Java Programming

a.length

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Strings

C Programming

'\0'

-terminated character array

Java Programming

String

built-in immutable data type

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Accessing a Library

C Programming

#include &lt;stdio.h&gt;

Java Programming

import java.io.File;

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Accessing a Library Function

C Programming

#include "math.h"
x = sqrt(2.2);

all function and variables names are global

Java Programming

x = Math.sqrt(2.2);

functions have different namespaces

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Printing

Printing to StdOut

C Programming

printf("sum = %d", x);

Java Programming

System.out.println("sum = " + x);

Formatted Printing to StdOut

C Programming

printf("avg = %3.2f", avg);

Java Programming

System.out.printf("avg = %3.2f", avg)

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Reading from StdIn

C Programming

scanf("%d", &x);

Java Programming

BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String s = in.readLine();

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Manipulating Pointers

C Programming

 *, &, +

Java Programming

no direct manipulation permitted

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Functions

C Programming

int max(int a, int b)

Java Programming

public static int max(int a, int b)

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Pass by Value

C Programming

primitive data types, structs, and pointers
are passed by value; array decays to pointer

Java Programming

all primitive data types and references (which includes
arrays), are passed by value

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Defining a Data Structure

C Programming

struct

Java Programming

class

key difference is language
support for defining methods to manipulate data

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Accessing a Data Structure

C Programming

a.numerator

Java Programming

a.numerator

for instance variables,

c = a.plus(b)

for methods

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Pointer Chasing

C Programming

x->left->right

Java Programming

x.left.right

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Allocating Memory

C Programming

malloc

Java Programming

new

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De-Allocating Memory

C Programming

free

Java Programming

automatic garbage collection

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Memory Allocation of Data Structures

C Programming

heap, stack, data, or bss

Java Programming

heap, with a little stack use

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Buffer Overflow

C Programming

segmentation fault, core dump, unpredicatable program

Java Programming

checked run-time error exception

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Declaring Constants

C Programming

const

and

#define

Java Programming

final

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Variable Auto-Initialization

C Programming

not guaranteed

Java Programming

instance variables (and array elements) initialized to 0, null, or
false, compile-time error to access uninitialized variables

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Data Hiding

C Programming

opaque pointers and 

static

Java Programming

private

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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)

Original Source: http://introcs.cs.princeton.edu/java/faq/c2java.html

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