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Update java.html.markdown
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Jake Prather
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---
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language: java
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author: Jake Prather
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author_url: http://github.com/JakeHP
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---
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Java is a general-purpose, concurrent, class-based, object-oriented computer programming language.
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Read more here: https://en.wikipedia.org/wiki/Java_(programming_language)
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```java
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// Single-line comments start with //
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/*
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Multi-line comments look like this.
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*/
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// Import Packages
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import java.util.ArrayList;
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import package.path.here;
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// Import "sub-packages"
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import java.lang.Math.*;
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// Your program's entry point is a function called main
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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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// General
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///////////////////////////////////////
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// Single-line comments start with //
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/*
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Multi-line comments look like this.
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*/
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// Import Packages
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import java.util.ArrayList;
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import package.path.here;
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// Import all "sub-packages"
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import java.lang.Math.*;
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// Your program's entry point is a function called main
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public class Main
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{
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//stuff here
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public static void main (String[] args) throws java.lang.Exception
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{
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//stuff here
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}
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}
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}
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// Printing
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System.out.println("Hello World");
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System.out.println("Integer: "+10+"Double: "+3.14+ "Boolean: "+true);
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// Printing, and forcing a new line on next print = println()
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System.out.println("Hello World");
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System.out.println("Integer: "+10+"Double: "+3.14+ "Boolean: "+true);
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// Printing, without forcing a new line on next print = print()
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System.out.print("Hello World");
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System.out.print("Integer: "+10+"Double: "+3.14+ "Boolean: "+true);
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///////////////////////////////////////
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// Types
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///////////////////////////////////////
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// Byte - 8-bit signed two's complement integer (-128 <= byte <= 127)
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// Short - 16-bit signed two's complement integer (-32,768 <= short <= 32,767)
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//Integer - 32-bit signed two's complement integer (-2,147,483,648 <= int <= 2,147,483,647)
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int x = 1;
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//Long - 64-bit signed two's complement integer (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807)
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//Float - Single-precision 32-bit IEEE 754 Floating Point
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//Double - Double-precision 64-bit IEEE 754 Floating Point
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//Boolean - True & False
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//Char - A single 16-bit Unicode character
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// Other than char, which is always 1 byte, these types vary in size depending
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// on your machine. sizeof(T) gives you the size of a variable with type T in
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// bytes so you can express the size of these types in a portable way.
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// For example,
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printf("%d\n", sizeof(int)); // => 4 (on machines with 4-byte words)
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// Arrays must be initialized with a concrete size.
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char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes
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int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes
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// (assuming 4-byte words)
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// You can initialize an array to 0 thusly:
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char my_array[20] = {0};
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// Indexing an array is like other languages -- or,
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// rather, other languages are like C
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my_array[0]; // => 0
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// Arrays are mutable; it's just memory!
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my_array[1] = 2;
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printf("%d\n", my_array[1]); // => 2
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// Strings are just arrays of chars terminated by a NUL (0x00) byte,
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// represented in strings as the special character '\0'.
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// (We don't have to include the NUL byte in string literals; the compiler
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// inserts it at the end of the array for us.)
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char a_string[20] = "This is a string";
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printf("%s\n", a_string); // %s formats a string
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/*
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You may have noticed that a_string is only 16 chars long.
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Char #17 is the NUL byte.
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Chars #18, 19 and 20 have undefined values.
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*/
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printf("%d\n", a_string[16]); => 0
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// Byte - 8-bit signed two's complement integer (-128 <= byte <= 127)
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byte foo = 100;
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// Short - 16-bit signed two's complement integer (-32,768 <= short <= 32,767)
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short bar = 10000;
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//Integer - 32-bit signed two's complement integer (-2,147,483,648 <= int <= 2,147,483,647)
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int foo = 1;
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//Long - 64-bit signed two's complement integer (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807)
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long bar = 100000L;
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//Float - Single-precision 32-bit IEEE 754 Floating Point
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float foo = 234.5f;
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//Double - Double-precision 64-bit IEEE 754 Floating Point
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double bar = 123.4;
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//Boolean - True & False
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boolean foo = true;
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boolean bar = false;
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//Char - A single 16-bit Unicode character
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char foo = 'A';
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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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String foo = "Hello World!\nLine2!";
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System.out.println(foo);
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//Hello World!
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//Line2!
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//Arrays
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//The array size must be decided upon declaration
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//The format for declaring an array is follows:
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//<datatype> [] <var name> = new <datatype>[<array size>];
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int [] array = new int[10];
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String [] array = new String[1];
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boolean [] array = new boolean[100];
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// Indexing an array - Accessing an element
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array[0];
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// Arrays are mutable; it's just memory!
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array[1] = 1;
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System.out.println(array[1]); // => 1
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array[1] = 2;
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printf("%d\n", my_array[1]); // => 2
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//Others to check out
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//ArrayLists - Like arrays except more functionality is offered, and the size is mutable
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//LinkedLists
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//Maps
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//HashMaps
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///////////////////////////////////////
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// Operators
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///////////////////////////////////////
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int i1 = 1, i2 = 2; // Shorthand for multiple declaration
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float f1 = 1.0, f2 = 2.0;
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// Arithmetic is straightforward
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i1 + i2; // => 3
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i2 - i1; // => 1
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i2 * i1; // => 2
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i1 / i2; // => 0 (0.5, but truncated towards 0)
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f1 / f2; // => 0.5, plus or minus epsilon
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// Modulo is there as well
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11 % 3; // => 2
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// Comparison operators are probably familiar, but
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// there is no boolean type in c. We use ints instead.
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// 0 is false, anything else is true. (The comparison
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// operators always return 0 or 1.)
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3 == 2; // => 0 (false)
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3 != 2; // => 1 (true)
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3 > 2; // => 1
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3 < 2; // => 0
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2 <= 2; // => 1
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2 >= 2; // => 1
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// Logic works on ints
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!3; // => 0 (Logical not)
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!0; // => 1
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1 && 1; // => 1 (Logical and)
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0 && 1; // => 0
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0 || 1; // => 1 (Logical or)
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0 || 0; // => 0
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// Bitwise operators!
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~0x0F; // => 0xF0 (bitwise negation)
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0x0F & 0xF0; // => 0x00 (bitwise AND)
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0x0F | 0xF0; // => 0xFF (bitwise OR)
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0x04 ^ 0x0F; // => 0x0B (bitwise XOR)
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0x01 << 1; // => 0x02 (bitwise left shift (by 1))
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0x02 >> 1; // => 0x01 (bitwise right shift (by 1))
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int i1 = 1, i2 = 2; // Shorthand for multiple declarations
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// Arithmetic is straightforward
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i1 + i2; // => 3
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i2 - i1; // => 1
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i2 * i1; // => 2
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i1 / i2; // => 0 (0.5, but truncated towards 0)
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// Modulo
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11 % 3; // => 2
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// Comparison operators
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3 == 2; // => 0 (false)
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3 != 2; // => 1 (true)
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3 > 2; // => 1
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3 < 2; // => 0
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2 <= 2; // => 1
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2 >= 2; // => 1
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// Bitwise operators!
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~ Unary bitwise complement
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<< Signed left shift
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>> Signed right shift
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>>> Unsigned right shift
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& Bitwise AND
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^ Bitwise exclusive OR
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| Bitwise inclusive OR
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///////////////////////////////////////
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// Control Structures
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///////////////////////////////////////
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if (0) {
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printf("I am never run\n");
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} else if (0) {
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printf("I am also never run\n");
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} else {
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printf("I print\n");
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}
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if (false) {
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System.out.println("I never run");
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} else if (false) {
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System.out.println("I am also never run");
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} else {
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System.out.println("I print");
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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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printf("\n");
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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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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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// 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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printf("\n");
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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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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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