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 promotionpromote 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 | | | short a=2,b=3,z;z=a*b; | a*b -> int |
x++ and ++xint 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 enum1. 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:
....
} |
enumWhy 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 |
| | Assignmentsassignment 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 examplepublic 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;
}
} |
Java Statementif (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 Switchswitch (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 Whilewhile (...) { .. increate conunter ...} | do {....} wjile (....) | execute >=1 times | infinity loop | while (true) {} |
| | for loopfor ( 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 ControlNested 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 |
Scopeif, while,for loop define local scope | vaiable declared inside control block could not used out of {} |
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