| 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) |
