Free Guides
Language Tutorials
SUN
Index
Language fundamentals
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Identifier is composed of a sequence of characters, where each character could be either a letter, currency symbol, digit or connecting punctuation. However first character cant be a digit.
Examples of illegal identifiers : 48chevy, all@hands, grand-sum -
Keywords
|
abstract |
default |
implements |
protected |
throw |
|---|---|---|---|---|
|
assert |
do |
import |
public |
throws |
|
boolean |
double |
instanceof |
return |
transient |
|
break |
else |
int |
short |
try |
|
byte |
extends |
interface |
static |
void |
|
case |
final |
long |
strictfp |
volatile |
|
catch |
finally |
native |
super |
while |
|
char |
float |
new |
switch |
|
|
class |
for |
package |
synchronize |
|
|
continue |
if |
private |
This |
|
- Reserved Literals :
|
null |
true |
false |
|---|
- Reserved Keywords not currently in use :
|
const |
goto |
|---|
-
synchronized, abstract, strictfp and native can only be applied to methods. transient and volatile can only be applied to variables. static and final can be applied to both.
-
The class containing at least one abstract method has to be declared as abstract. However an abstract class need not have any abstract methods in it.
-
Literal denotes a constant values :
-
Integer Literals int, long, byte, short,octal, hexadecimal
-
Floating point Literals suffix f or F, d or D; exponent notation 1.2E-2
-
Boolean Literals true or false
-
Character Literals single quotes, hexadecimal with prefix \u, \ddd where ddd is octal
-
String Literals double quotes
-
-
Comment are of three types :
-
single line // ... to end of line
-
multiple line /* ... */
-
javadoc comment /** ... */
-
-
Comment start sequences are ignored when occurring inside comments, hence making nesting of comments impossible.
-
Primitive Data Types
|
byte |
8 bits |
-27 |
+27-1 |
Boolean |
|---|---|---|---|---|
|
short |
16 bits |
-215 |
+215-1 |
Short |
|
int |
32 bits |
-231 |
+231-1 |
Integer |
|
long |
64 bits |
-263 |
+263-1 |
Long |
|
char |
16 bits |
0x0 |
0xffff |
Character |
|
float |
32 bits |
|
|
Float |
|
double |
64 bits |
|
|
Double |
|
boolean |
|
true or false only |
Boolean |
|
-
Default values for fields are false, '\u0000', 0L, 0, 0.0F, 0.0D and null. All static, instance variables as well as object references are automatically initialized. Local variables and object references need to be explicitly initialized before use.
-
If a reference is set to null, then the program will compile but throw a NullPointerException at runtime.