String class API
Important String class constructors
1.String(byte[] bytes) --- byte[] ----> String converter
2.String(char[] chars) --- char[] ---> String converter
3.String (byte[] bytes,int offset,int length) ---byte[] ----> String converter from the specified offset , specified length no of bytes will be converted.
eg . String s=new String(bytes,3,4); --- String will contain bytes[3]----bytes[6]
4. String(char[] ch,int offset,int length)
5. String(String s)
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| String Handling in JAVA |
String class methods --- to go through
charAt,compareTo,contains,copyValueOf,format,valueOf,getBytes,toCharArray,toLowerCase,indexOf,lastIndexOf,split,replace,startsWith,endsWith,length,intern
1. boolean equals(Object o) ---- ret true iff 2 strings are having same contents (case sensitive)
About equals()
super class def. --- java.lang.Object
public boolean equals(Object o)
Returns true if both refs(this & o) are equal i.e referring to the same object.
Sub-class developers MUST override equals for content-wise(depending on Object's state) comparison.
2. concat,charAt,indexOf,lastIndexOf,toUpperCase,toLowerCase,format,split
printf & Formater class
Refer to java.util.Formatter class for formatting conversion details.
Imp ---
Formatting details
%c -- character
%b -- boolean
%h -- hex value of hashcode of obj ref.
%s -- string
%d -- int
%f,%g -- float/double
%x -- hex value
%n -- line separator
%tD -- Date
%tT -- Time
%tc -- Time stamp(date & Time)
%td-%1$tb-%1$tY -- can be applied to GC or Date.
Date/Time Handling in Java
API
1. java.util.Date--- represents system date.
Constructor
1.Date() --- creates Date class instance representing system date.
2.Date(long msec) --- creates Date class instance representing date for msec elapsed after epoch(=1st Jan 1970)
2. java.util.GregorianCalendar
month range --- 0-11
GregorianCalendar(int yr,int mon,int date);
GregorianCalendar(int yr,int mon,int date,int hr,int min,int sec);
3. Date/Time formatting via printf
%tc -- for complete timestamp(date & time)
%tD -- for date
%tT -- time
Arguments --- Date, GregorianCalendar
static import syntax ---
eg -- import static java.util.Calendar.*;
or import static java.lang.System.*;
in such src - u can access directly static members of Calendar class or from 2nd statement u can directly use out.println("testing static imports!");
var-args
variable args syntax.--- Must be last arg in the method args.
Can use primitive type or ref types.
Legal ---
void doStuff(int... x) { } // expects from 0 to many ints
Usage : ref.doStuff();
int[] ints={1,2,3,4};
ref.doStuff(ints);
ref.doStuff(20,34,56);
System.out.printf("%n");
// as parameters
void doStuff2(char c, int... x) { } // expects first a char,
// then 0 to many ints
void doStuff3(Animal... animal) { } // 0 to many Animals
invocations ---
ref.doStuff3();
ref.doStuff3(Animal[] animals);
ref.doStuff3(Animal a1,Animal a2,Animal a3);
Illegal:
void doStuff4(int x...) { } // bad syntax
void doStuff5(int... x, char... y) { } // too many var-args
void doStuff6(String... s, byte b) { } // var-arg must be last
Generic syntax ---
Available from Java SE 5 onwards.
Represents Parameterized Types.
Can Create Generic classes, interfaces, methods and constructors.
Operates on Parameterized data Types
In Pre-generics world , similar achieved via Object class reference.
Advantages
Adds Type Safety to the code @ compile time
Can add type safe code where type-mismatch errors are caught at compile time.
No need of explicit type casting, as all casts are automatic and implicit.
A generic class means that the class declaration includes a type parameter.
eg --- class MyGeneric<T>
T ---type --- ref type
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