Operators
[] () |
x++ x-- |
post unary |
++x --x |
pre unary |
~ + - ! |
! only for logic |
* / % |
+ - |
<<>>>>> |
shift |
<> <= >= instanceof |
compare |
== != |
for primitives, obj type compare addr |
&- ^ ->| |
logic |
&& -> || |
shortcut logic |
(boolean)?x :y |
tenary (can be nested) |
= |
assignment |
+= -=... |
compound assignment, auto casting |
casting (type) |
== and != are logic; = is assignment
. operator precedent of casting, so be careful with (B a).m() vs (B)a.m()
Numberic promotion
promote the larger operand type |
byte,short,char ->int->float->double |
assign result to promoted type |
1)unary exclusive short ++ -> still short |
2) by default literal is int or double |
float f=1; |
ok,1 is a definite number |
float f=0.1; |
X 0.1 is not definite number |
long l=power(2,32) |
X Integer.MAX_VALUE=power(2,32)-1 |
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short a=2,b=3,z;z=a*b; |
a*b -> int |
x++ and ++x
int x=3,y; |
y=x++; |
assign x to y(1), then increment x(2) |
y=++x; |
increment x(2), then assign x to y(2) |
y=++x*5/x-- + --x; |
x=2,y=7 |
No effect in stand for loop |
Using enum
1. dot notation, Days.FRIDAY
2. name(), toString() ->capital label
3. ordinal() -> index from 0
4. valueOf(String) ->parse string to enum
5. compare: == or equals()
6.switch (enum_var) {
case enum_value:
..
default:
....
}
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enum
Why enum? |
more readable constant declaration |
allow compiler time check |
avoid unexpected behavior |
document upfront |
What's enum |
start from java5 |
extends java.lang.enum |
enum constant internally implemented as public static final variables |
overriden equals(), toString, hasCode() |
may define variable,constructor, methods just like in a class |
name(),toString() return string value |
ordinal() return index |
could has constuctor and methods, just like a class |
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Assignments
assignment overflow ( too high to hold) |
int i=1.0;byte b=128;float f=0.1; |
explicit cast required when overflow |
underflow (float number too small to represent) |
Compound assignment |
auto cast back to left operand |
assignment chaining allowed |
int i,j,k; i=j=k=9; |
if (a=9) {} //exception |
if (a=true){} //ok |
enum example
public enum Days {
SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY, SATURDAY;
}
// syntax like class, but with enum keyword
// name=capital label;ordinal=index value from 0
// could have fields/constructor/methods inside
// extends java.lang.enum
// implemented internally as class,
// enum value are public static final object constant
public enum MusicType{
CLASSIC(1),JAZZ(4),ROCK(6),METAL(11);
private int earDamageFacor;
private MusicType(int earDamageFactor)
{ this earDamageFactor=earDamageFactor; }
public int calcHearingLoss(int huors)
{ return huors*earDamageFactor;}
public String toString ()
{ return this.name()+"-"+this.ordinal()+'_"
+ this.earDamageFactor;
}
}
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Java Statement
if (boolean) {} |
multiple statement need {} |
else if (...) {} |
one statement may miss {} |
else {} |
( ...) ? x :y |
x,y: same data type |
... ? ...?x :y:z |
nested |
if (x=5) {} //won't compile
Switch
switch (literal-value) { |
Byte,byte,Short,short,Integer,int |
case 1: ....;break; |
Character,char,enum,String |
case 2: ....;break; |
8 types, after case is literal |
case 0: ....;break; |
default: position not matters |
default: |
breaks; avoid follow through, need in every case, exclude last on |
} |
the case value must be compiling time literal
While
while (...) { .. increate conunter ...} |
do {....} wjile (....) |
execute >=1 times |
infinity loop |
while (true) {} |
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for loop
for ( int i;i<arr.length-1;i++) |
standard for loop: (4 steps init ->eval ->body exec ->increament, ++i,i++ no different) |
multiple declaration initializer allowed, separated by ',', should be same type |
initializer scope: inside for loop |
for ( Class instance:collection){} |
for each: iterate only, unable to access i |
java.iterable <-java.lamg.collection |
Array, ArrayList, List |
for(;;){} |
infinite loop |
for( int i=0;i<10;) {i=i++;} |
infinite loop |
for ( int value, values) {} -> for ( java.uitl.iterator(Integer) i=value.iterator(); i.hasNext()){}
Advance Flow Control
Nested loops |
Optional label |
OUTER_LOOP:.... INNER_LOOP |
all flow control allowed, but bad practice |
breaks optional_label; |
not for if..then..else |
breakout current block |
breakout current block and go to optional label |
Continue optional_label; |
not for if..then..else and switch |
stop and Continue next iteration |
stop and go to optional label |
Scope
if, while,for loop define local scope |
vaiable declared inside control block could not used out of {} |
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