Java Syntax

Syntax

The most common integer type is int.

Integer: if you type 4, you get an int with value 4. Usually programmers use int by default.
Java is strongly typed - every variable and every expression has a type that is known at compile time.
If you want it to be a long, you need to add an L (or lowercase l) at the end of the number.
long myNumber = 12345678900L;

Examples of some other "keystrokes" (special escape sequences) represented in Java:

\t (tab)
\b (backspace)
\n (linefeed)
\r (carriage return)
\f (form feed)
\" (double quote)
\' (single quote)
\\ (backslash)

String (** actually this is a class: java.lang.String )

"This is a string literal"
Strings are immutable - values cannot be changed after creation (they are not simple arrays of characters as in C++) Each String constant results in a String object

String str = "Sun is Hot"; String sun = str.substring(0,3); String java = "Java"; String str2 = java + str.substring(3, str.length() ); // (last one exclusive) int len = "HotJava".length(); String objstr = obj.toString(); System.out.println ("obj");

**Notice: When you use a String literal in a Java program, Java automatically creates an instance of a the class String.
So,
a = = "" ;    // can never be true since "" creates a new empty string
This used to be true but is not anymore. Interesting.

Note: can concatenate, and work with substrings, but cannot change specific chars in a string

Discussion on strings and how differ from C - Core Java : Chapter 3

More on StringBuffer class later

Reference types (Classes, Interfaces, Arrays)

Arrays

char s[]; //this is an array s of char's int [] array1; //this is an array array1 of int's

optional placement of []

You can even build arrays of arrays:

int table [] [] = new int [5] [6];

Array boundaries are checked at run-time to avoid overflowing a stack and corrupting memory.

int [] a = new int [5] /* leave space for 5 int */

T [] b = new T [5] /*leaves space for 5 references to T's - not 5 T's*/

int list [] = new int [50];

String names [] = {"Joe","Sue","Molly","Maggie","Taj"};

String names []; names = new String [5]; names[0] = new String ("Joe"); names[1] = new String ("Sue"); names[2] = new String ("Molly"); names[3] = new String ("Maggie"); names[4] = new String ("Taj");

You cannot create static arrays at compile time:

int list [50]; // will generate a compiler error

int list []; for (int i=0, i < 4; i++) { list[i] = i; }

Aside: From Core Java, Of course, while it is true that the ++ operator gives the C++ language its name, it also led to the first joke about the language. C++ haters point out that even the name of the language contains a bug: "After all, it should really be called ++C, since we only want to use a language after it has been improved."

You can also declare and initialize non-rectangular arrays with nested initializations

static int[][] twodim = { {1,2},{3,4,5},{5,6,7,8} }

Flow Control

Branching

if/else (must be Boolean: not 0 or 1)

if (Boolean) { statements; } else { statements; } if (a instanceof b) ...

switch (expr1) { case expr2: statements; break; case expr3: statements; break; default: statements; break; }

expressions must be constants: int, byte, short or char (convertable via casting to int (automatic promotion) )

casting aside: ((Circle)this).r ;

public static final int YES = 0, NO = 1, CANCEL = 2;

They are constant since final says no one can change them

If no breaks, drop-through (once match, executes all below)

do { statements; } while (Boolean);

int x = 1; do { System.out.println("Looping, round " + x); x++; } while (x <= 4); Looping, round 1 Looping, round 2 Looping, round 3 Looping, round 4

for (init expr; test expr2; increment expr3) { statements; } for ( i=1 ; i < 10 ; i++) (start, stop, increment)

Enhanced for

public static void main(String[] args){ int[] numbers = {1,2,3,4,5,6,7,8,9,10}; for (int item : numbers) { System.out.println("Count is: " + item); }

int count; for (count = 1; count <= 12; count++) { switch (count % 3) { // mod 3 case 0: g.setColor(Color.red); break; case 1: g.setColor(Color.blue); break; case 2: g.setColor(Color.green); break; } g.drawLine(10, count * 10 , 80, count * 10); }

General

break [label] continue [label] return expr; label: statement; //breaks in loops - pop out of greater than inner loop out: for (int i = 1; i <= 5; i++) for (int j = 1; j <= 3; j++) { System.out.println("i is " + i + " , j is " + j); if ((i + j) > 4) break out; } // jumps out both loops System.out.println("end of loops");

i is 1, j is 1 i is 1, j is 2 i is 1, j is 3 i is 2, j is 1 i is 2, j is 2 i is 2, j is 3 end of loops

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Inside scoop:
java file - javap - byte code disassembler- located at 0xCAFEBABE
Next, Instance Variables and Methods, Constructors, Finalizers