String
a sequence of characters, implimented as array |
create using 1) constructor new String("") 2) literals 3)concatenation |
empty string "" |
Concatenation
if anyone of operand is string, all other operands are cast to String |
toString() for reference type |
primary is convert directly to string |
If none of operand is String, the return will not be string |
int x=3;y=4; String s=x+y; // error can not assign int to String |
Default toString() return memory address for Object class: class name@memoryaddress
Compare String
== |
memory location, only for test |
equals();equalsIgnoreCase() |
content |
compareTo() |
content |
Immutability and String Pool
Once initialized, never changed again, Chain of methods results in multiple Strings |
String literals could be a largest chuck of memory. |
String pool |
string literals,literal concatenation ( compiler time) |
obj.intern(): will return a string in string pool or added if not exist |
String s = "Hel" + lo;//runtime concatenation, not using string pool |
Math, Wrapper class, String: immutable
Math,Wrapper, String, StringBuilder,System: final
Methods
length() |
method instead of attribute, trade-offspace and performance |
charAt() |
StringIndexOutOfBoundsException |
indexOf() |
0..length()-1, -1 |
substring(begin,end) |
[ ...), exception, empty string |
toLowerCase() |
toUpperCase() |
startWith() |
endWith() |
s1.contains(s2) |
s.indexOf(s2) !=-1 |
replace(oldChar,newChar) |
replace(oldCharSeq,newCharSeq) |
character sequence - String, StringBuilder |
trim() |
trim white space |
|
|
Why StringBuilder
efficient memory usage |
Mutable and chain of operation will result in one sb |
before java5, StringBuffer was used, but slower due to thread safe. |
Create a StringBuilder
new StringBuilder(); |
new StringBuilder( sb2 ); |
new StringBuilder(5); |
size()=0; capacity=5 |
SringBuider Methods
append(str) |
insert(offset,str) |
delete(from,to) |
[from,to) |
deleteCharAt() |
reverse() |
toString() |
sb for performance, convert to string in the end |
subString(int), subString(int,int) |
returns string type |
CharAt();indexOf();length();substring() see String class
equals() is not overriden in StringBuilder, use toString().equals(s1);
|
|
|
