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| -rw-r--r-- | java.html.markdown | 290 |
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diff --git a/java.html.markdown b/java.html.markdown index 48e1ff36..0ca36132 100644 --- a/java.html.markdown +++ b/java.html.markdown @@ -1,177 +1,175 @@ --- + language: java + author: Jake Prather + author_url: http://github.com/JakeHP + --- Java is a general-purpose, concurrent, class-based, object-oriented computer programming language. Read more here: https://en.wikipedia.org/wiki/Java_(programming_language) ```java -// Single-line comments start with // -/* -Multi-line comments look like this. -*/ - -// Import Packages -import java.util.ArrayList; -import package.path.here; -// Import "sub-packages" -import java.lang.Math.*; - -// Your program's entry point is a function called main -public class Main -{ - public static void main (String[] args) throws java.lang.Exception +/////////////////////////////////////// +// General +/////////////////////////////////////// + // Single-line comments start with // + /* + Multi-line comments look like this. + */ + + // Import Packages + import java.util.ArrayList; + import package.path.here; + // Import all "sub-packages" + import java.lang.Math.*; + + // Your program's entry point is a function called main + public class Main { - //stuff here + public static void main (String[] args) throws java.lang.Exception + { + //stuff here + } } -} - -// Printing -System.out.println("Hello World"); -System.out.println("Integer: "+10+"Double: "+3.14+ "Boolean: "+true); + + // Printing, and forcing a new line on next print = println() + System.out.println("Hello World"); + System.out.println("Integer: "+10+"Double: "+3.14+ "Boolean: "+true); + // Printing, without forcing a new line on next print = print() + System.out.print("Hello World"); + System.out.print("Integer: "+10+"Double: "+3.14+ "Boolean: "+true); /////////////////////////////////////// // Types /////////////////////////////////////// -// Byte - 8-bit signed two's complement integer (-128 <= byte <= 127) - -// Short - 16-bit signed two's complement integer (-32,768 <= short <= 32,767) - -//Integer - 32-bit signed two's complement integer (-2,147,483,648 <= int <= 2,147,483,647) -int x = 1; - -//Long - 64-bit signed two's complement integer (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807) - -//Float - Single-precision 32-bit IEEE 754 Floating Point - -//Double - Double-precision 64-bit IEEE 754 Floating Point - -//Boolean - True & False - -//Char - A single 16-bit Unicode character - - -// Other than char, which is always 1 byte, these types vary in size depending -// on your machine. sizeof(T) gives you the size of a variable with type T in -// bytes so you can express the size of these types in a portable way. -// For example, -printf("%d\n", sizeof(int)); // => 4 (on machines with 4-byte words) - -// Arrays must be initialized with a concrete size. -char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes -int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes - // (assuming 4-byte words) - - -// You can initialize an array to 0 thusly: -char my_array[20] = {0}; - -// Indexing an array is like other languages -- or, -// rather, other languages are like C -my_array[0]; // => 0 - -// Arrays are mutable; it's just memory! -my_array[1] = 2; -printf("%d\n", my_array[1]); // => 2 - -// Strings are just arrays of chars terminated by a NUL (0x00) byte, -// represented in strings as the special character '\0'. -// (We don't have to include the NUL byte in string literals; the compiler -// inserts it at the end of the array for us.) -char a_string[20] = "This is a string"; -printf("%s\n", a_string); // %s formats a string - -/* -You may have noticed that a_string is only 16 chars long. -Char #17 is the NUL byte. -Chars #18, 19 and 20 have undefined values. -*/ - -printf("%d\n", a_string[16]); => 0 + // Byte - 8-bit signed two's complement integer (-128 <= byte <= 127) + byte foo = 100; + + // Short - 16-bit signed two's complement integer (-32,768 <= short <= 32,767) + short bar = 10000; + + //Integer - 32-bit signed two's complement integer (-2,147,483,648 <= int <= 2,147,483,647) + int foo = 1; + + //Long - 64-bit signed two's complement integer (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807) + long bar = 100000L; + + //Float - Single-precision 32-bit IEEE 754 Floating Point + float foo = 234.5f; + + //Double - Double-precision 64-bit IEEE 754 Floating Point + double bar = 123.4; + + //Boolean - True & False + boolean foo = true; + boolean bar = false; + + //Char - A single 16-bit Unicode character + char foo = 'A'; + + //Strings + String foo = "Hello World!"; + // \n is an escaped character that starts a new line + String foo = "Hello World!\nLine2!"; + System.out.println(foo); + //Hello World! + //Line2! + + //Arrays + //The array size must be decided upon declaration + //The format for declaring an array is follows: + //<datatype> [] <var name> = new <datatype>[<array size>]; + int [] array = new int[10]; + String [] array = new String[1]; + boolean [] array = new boolean[100]; + + // Indexing an array - Accessing an element + array[0]; + + // Arrays are mutable; it's just memory! + array[1] = 1; + System.out.println(array[1]); // => 1 + array[1] = 2; + printf("%d\n", my_array[1]); // => 2 + + //Others to check out + //ArrayLists - Like arrays except more functionality is offered, and the size is mutable + //LinkedLists + //Maps + //HashMaps /////////////////////////////////////// // Operators /////////////////////////////////////// -int i1 = 1, i2 = 2; // Shorthand for multiple declaration -float f1 = 1.0, f2 = 2.0; - -// Arithmetic is straightforward -i1 + i2; // => 3 -i2 - i1; // => 1 -i2 * i1; // => 2 -i1 / i2; // => 0 (0.5, but truncated towards 0) - -f1 / f2; // => 0.5, plus or minus epsilon - -// Modulo is there as well -11 % 3; // => 2 - -// Comparison operators are probably familiar, but -// there is no boolean type in c. We use ints instead. -// 0 is false, anything else is true. (The comparison -// operators always return 0 or 1.) -3 == 2; // => 0 (false) -3 != 2; // => 1 (true) -3 > 2; // => 1 -3 < 2; // => 0 -2 <= 2; // => 1 -2 >= 2; // => 1 - -// Logic works on ints -!3; // => 0 (Logical not) -!0; // => 1 -1 && 1; // => 1 (Logical and) -0 && 1; // => 0 -0 || 1; // => 1 (Logical or) -0 || 0; // => 0 - -// Bitwise operators! -~0x0F; // => 0xF0 (bitwise negation) -0x0F & 0xF0; // => 0x00 (bitwise AND) -0x0F | 0xF0; // => 0xFF (bitwise OR) -0x04 ^ 0x0F; // => 0x0B (bitwise XOR) -0x01 << 1; // => 0x02 (bitwise left shift (by 1)) -0x02 >> 1; // => 0x01 (bitwise right shift (by 1)) + int i1 = 1, i2 = 2; // Shorthand for multiple declarations + + // Arithmetic is straightforward + i1 + i2; // => 3 + i2 - i1; // => 1 + i2 * i1; // => 2 + i1 / i2; // => 0 (0.5, but truncated towards 0) + + // Modulo + 11 % 3; // => 2 + + // Comparison operators + 3 == 2; // => 0 (false) + 3 != 2; // => 1 (true) + 3 > 2; // => 1 + 3 < 2; // => 0 + 2 <= 2; // => 1 + 2 >= 2; // => 1 + + // Bitwise operators! + ~ Unary bitwise complement + << Signed left shift + >> Signed right shift + >>> Unsigned right shift + & Bitwise AND + ^ Bitwise exclusive OR + | Bitwise inclusive OR /////////////////////////////////////// // Control Structures /////////////////////////////////////// -if (0) { - printf("I am never run\n"); -} else if (0) { - printf("I am also never run\n"); -} else { - printf("I print\n"); -} - -// While loops exist -int ii = 0; -while (ii < 10) { - printf("%d, ", ii++); // ii++ increments ii in-place, after using its value. -} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " - -printf("\n"); - -int kk = 0; -do { - printf("%d, ", kk); -} while (++kk < 10); // ++kk increments kk in-place, before using its value -// => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " - -printf("\n"); - -// For loops too -int jj; -for (jj=0; jj < 10; jj++) { - printf("%d, ", jj); -} // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " + if (false) { + System.out.println("I never run"); + } else if (false) { + System.out.println("I am also never run"); + } else { + System.out.println("I print"); + } + } -printf("\n"); + // While loops exist + int ii = 0; + while (ii < 10) { + printf("%d, ", ii++); // ii++ increments ii in-place, after using its value. + } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " + + printf("\n"); + + int kk = 0; + do { + printf("%d, ", kk); + } while (++kk < 10); // ++kk increments kk in-place, before using its value + // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " + + printf("\n"); + + // For loops too + int jj; + for (jj=0; jj < 10; jj++) { + printf("%d, ", jj); + } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " + + printf("\n"); /////////////////////////////////////// // Typecasting |