| 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 "); 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 | ' '-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) |