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Update java.html.markdown
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Jake Prather
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@ -71,6 +71,9 @@ Read more here: https://en.wikipedia.org/wiki/Java_(programming_language)
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//Char - A single 16-bit Unicode character
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char foo = 'A';
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//Make a variable a constant
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final int HOURS_I_WORK_PER_WEEK = 9001;
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//Strings
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String foo = "Hello World!";
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// \n is an escaped character that starts a new line
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@ -133,6 +136,13 @@ Read more here: https://en.wikipedia.org/wiki/Java_(programming_language)
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& Bitwise AND
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^ Bitwise exclusive OR
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| Bitwise inclusive OR
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// Incrementations
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int i=0;
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i++; //i = 1. Post Incrementation
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++i; //i = 2. Pre Incrementation
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i--; //i = 1. Post Decrementation
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--i; //i = 0. Pre Decrementation
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///////////////////////////////////////
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// Control Structures
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@ -147,206 +157,125 @@ Read more here: https://en.wikipedia.org/wiki/Java_(programming_language)
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}
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}
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// While loops exist
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int ii = 0;
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while (ii < 10) {
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printf("%d, ", ii++); // ii++ increments ii in-place, after using its value.
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} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
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// While loop
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int i = 0;
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while(i < 100){
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System.out.println(i);
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//Increment the counter
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i++;
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}
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printf("\n");
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// Do While Loop
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int i = 0;
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do{
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System.out.println(i);
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//Increment the counter
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i++;
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}while(i < 100);
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int kk = 0;
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do {
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printf("%d, ", kk);
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} while (++kk < 10); // ++kk increments kk in-place, before using its value
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// => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
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// For Loop
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int i;
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//for loop structure => for(<start_statement>;<conditional>;<step>)
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for(i=0;i<100;i++){
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System.out.println(i);
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}
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printf("\n");
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// For loops too
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int jj;
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for (jj=0; jj < 10; jj++) {
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printf("%d, ", jj);
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} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "
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printf("\n");
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///////////////////////////////////////
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// Typecasting
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///////////////////////////////////////
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// Every value in C has a type, but you can cast one value into another type
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// if you want.
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int x_hex = 0x01; // You can assign vars with hex literals
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// Casting between types will attempt to preserve their numeric values
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printf("%d\n", x_hex); // => Prints 1
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printf("%d\n", (short) x_hex); // => Prints 1
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printf("%d\n", (char) x_hex); // => Prints 1
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// Types will overflow without warning
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printf("%d\n", (char) 257); // => 1 (Max char = 255)
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// Integral types can be cast to floating-point types, and vice-versa.
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printf("%f\n", (float)100); // %f formats a float
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printf("%lf\n", (double)100); // %lf formats a double
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printf("%d\n", (char)100.0);
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// Converting data
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//Convert String To Integer
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Integer.parseInt("123");//returns an integer version of "123"
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//Convert Integer To String
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Integer.toString(123);//returns a string version of 123
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//For other conversions check out the following classes:
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//Double
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//Long
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//String
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// You can also cast java objects, there's a lot of details and
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// deals with some more intermediate concepts.
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// Feel free to check it out here: http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
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///////////////////////////////////////
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// Pointers
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// Classes And Functions
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///////////////////////////////////////
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// A pointer is a variable declared to store a memory address. Its declaration will
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// also tell you the type of data it points to. You can retrieve the memory address
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// of your variables, then mess with them.
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// Classes Syntax shown below.
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// Function declaration syntax:
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// <public/private/protected> <return type> <function name>(<args>)
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// Here is a quick rundown on access level modifiers (public, private, etcetc) http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html
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int x = 0;
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printf("%p\n", &x); // Use & to retrieve the address of a variable
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// (%p formats a pointer)
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// => Prints some address in memory;
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public class Bicycle {
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// Bicycle's Fields/Variables
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public int cadence;
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public int gear;
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public int speed;
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// Constructors are a way of creating classes
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// This is a default constructor
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public Bicycle(){
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gear = 1;
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cadence = 50;
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startGear = 1;
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}
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// Pointer types end with * in their declaration
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int* px; // px is a pointer to an int
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px = &x; // Stores the address of x in px
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printf("%p\n", px); // => Prints some address in memory
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// To retreive the value at the address a pointer is pointing to,
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// put * in front to de-reference it.
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printf("%d\n", *px); // => Prints 0, the value of x, which is what px is pointing to the address of
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// You can also change the value the pointer is pointing to.
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// We'll have to wrap the de-reference in parenthesis because
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// ++ has a higher precedence than *.
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(*px)++; // Increment the value px is pointing to by 1
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printf("%d\n", *px); // => Prints 1
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printf("%d\n", x); // => Prints 1
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int x_array[20]; // Arrays are a good way to allocate a contiguous block of memory
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int xx;
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for (xx=0; xx<20; xx++) {
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x_array[xx] = 20 - xx;
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} // Initialize x_array to 20, 19, 18,... 2, 1
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// Declare a pointer of type int and initialize it to point to x_array
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int* x_ptr = x_array;
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// x_ptr now points to the first element in the array (the integer 20).
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// This works because arrays are actually just pointers to their first element.
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// Arrays are pointers to their first element
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printf("%d\n", *(x_ptr)); // => Prints 20
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printf("%d\n", x_array[0]); // => Prints 20
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// Pointers are incremented and decremented based on their type
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printf("%d\n", *(x_ptr + 1)); // => Prints 19
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printf("%d\n", x_array[1]); // => Prints 19
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// You can also dynamically allocate contiguous blocks of memory with the
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// standard library function malloc, which takes one integer argument
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// representing the number of bytes to allocate from the heap.
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int* my_ptr = (int*) malloc(sizeof(int) * 20);
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for (xx=0; xx<20; xx++) {
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*(my_ptr + xx) = 20 - xx; // my_ptr[xx] = 20-xx would also work here
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} // Initialize memory to 20, 19, 18, 17... 2, 1 (as ints)
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// Dereferencing memory that you haven't allocated gives
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// unpredictable results
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printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what?
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// When you're done with a malloc'd block of memory, you need to free it,
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// or else no one else can use it until your program terminates
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free(my_ptr);
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// Strings can be char arrays, but are usually represented as char
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// pointers:
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char* my_str = "This is my very own string";
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printf("%c\n", *my_str); // => 'T'
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function_1();
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} // end main function
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///////////////////////////////////////
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// Functions
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///////////////////////////////////////
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// Function declaration syntax:
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// <return type> <function name>(<args>)
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int add_two_ints(int x1, int x2){
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return x1 + x2; // Use return to return a value
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}
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/*
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Functions are pass-by-value, but you can make your own references
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with pointers so functions can mutate their values.
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Example: in-place string reversal
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*/
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// A void function returns no value
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void str_reverse(char* str_in){
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char tmp;
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int ii=0, len = strlen(str_in); // Strlen is part of the c standard library
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for(ii=0; ii<len/2; ii++){
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tmp = str_in[ii];
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str_in[ii] = str_in[len - ii - 1]; // ii-th char from end
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str_in[len - ii - 1] = tmp;
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}
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}
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/*
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char c[] = "This is a test.";
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str_reverse(c);
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printf("%s\n", c); // => ".tset a si sihT"
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*/
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///////////////////////////////////////
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// User-defined types and structs
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///////////////////////////////////////
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// Typedefs can be used to create type aliases
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typedef int my_type;
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my_type my_type_var = 0;
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// Structs are just collections of data
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struct rectangle {
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int width;
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int height;
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};
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void function_1(){
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struct rectangle my_rec;
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// Access struct members with .
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my_rec.width = 10;
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my_rec.height = 20;
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// You can declare pointers to structs
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struct rectangle* my_rec_ptr = &my_rec;
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// Use dereferencing to set struct pointer members...
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(*my_rec_ptr).width = 30;
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// ... or use the -> shorthand
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my_rec_ptr->height = 10; // Same as (*my_rec_ptr).height = 10;
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}
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// You can apply a typedef to a struct for convenience
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typedef struct rectangle rect;
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int area(rect r){
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return r.width * r.height;
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}
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// This is a specified constructor (it contains arguments)
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public Bicycle(int startCadence, int startSpeed, int startGear) {
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gear = startGear;
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cadence = startCadence;
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speed = startSpeed;
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}
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// the Bicycle class has
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// four methods
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public void setCadence(int newValue) {
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cadence = newValue;
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}
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public void setGear(int newValue) {
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gear = newValue;
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}
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public void applyBrake(int decrement) {
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speed -= decrement;
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}
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public void speedUp(int increment) {
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speed += increment;
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}
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}
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//Now..Later in the main / driver of your java program
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public class Main
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{
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public static void main (String[] args) throws java.lang.Exception
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{
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//Call bicycle's constructor
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Bicycle trek = new Bicycle();
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trek.speedUp(3);
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trek.setCadence(100);
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}
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}
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```
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## Further Reading
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Best to find yourself a copy of [K&R, aka "The C Programming Language"](https://en.wikipedia.org/wiki/The_C_Programming_Language)
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Another good resource is [Learn C the hard way](http://c.learncodethehardway.org/book/)
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Other than that, Google is your friend.
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Other Topics To Research:
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-Inheritance (http://en.wikipedia.org/wiki/Inheritance_(object-oriented_programming))
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-Abstraction (http://en.wikipedia.org/wiki/Abstraction_(computer_science))
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-Exceptions (http://en.wikipedia.org/wiki/Exception_handling)
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-Interfaces (http://en.wikipedia.org/wiki/Interfaces_(computer_science))
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-Generics (http://en.wikipedia.org/wiki/Generics_in_Java)
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The links provided are just to get an understanding of the topic, feel free to google and find specific examples
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