Normally, array is a collection of similar type of elements that have contiguous memory location.
Java array is an object the contains elements of similar data type. It is a data structure where we store similar elements. We can store only fixed set of elements in a java array.
Array in
java is index based, first element of the array is stored at 0 index.
Advantage of Java Array
- Code Optimization: It makes the code optimized, we can retrieve or sort the data easily.
- Random access: We can get any data located at any index position.
Disadvantage of Java Array
Size
Limit: We can store
only fixed size of elements in the array. It doesn't grow its size at runtime.
To solve this problem, collection framework is used in java. Best
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Types of Array in java
There are two types of array.- Single Dimensional Array
- Multidimensional Array
Single Dimensional Array
One dimensional array is
a list of variables of same type that are accessed by a common name. An individual variable in the array is called an
array element. Arrays forms a way to handle groups of related data.
Multidimensional
Array
In Java, multidimensional
arrays are actually arrays of arrays. These, as you might expect, look and
act like regular multidimensional arrays. However, as you will see, there are a
couple of subtle differences. To declare a multidimensional array variable,
specify each additional index using another set of square brackets. For
example, the following declares a two-dimensional array variable called twoD.
When you allocate memory for a
multidimensional array, you need only specify the memory for the first
(leftmost) dimension. You can allocate the remaining dimensions separately.
While there is no advantage to
individually allocating the second dimension arrays in this situation, there
may be in others. For example, when you allocate dimensions manually, you do
not need to allocate the same number of elements for each dimension. As stated
earlier, since multidimensional arrays are actually arrays of arrays, the
length of each array is under your control. For example, the following program
creates a two-dimensional array in which the sizes of the second dimension are
unequal. best
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Java Regex
The Java Regex or Regular Expression is an API to define pattern for searching or manipulating strings.It is widely used to define constraint on strings such as password and email validation. After learning java regex tutorial, you will be able to test your own regular expressions by the Java Regex Tester Tool.
Java Regex API provides 1 interface and 3 classes in java.util.regex package.
java.util.regex package
It provides following classes and interface for regular expressions. The Matcher and Pattern classes are widely used in java regular expression.
1. MatchResult interface
2. Matcher class
3. Pattern class
4. PatternSyntaxException class
Matcher class
It implements MatchResult interface. It is a regex engine i.e. used to perform match operations on a character sequence.|
No.
|
Method
|
Description
|
|
1
|
boolean matches()
|
test whether the regular
expression matches the pattern.
|
|
2
|
boolean find()
|
finds the next expression that
matches the pattern.
|
|
3
|
boolean find(int start)
|
finds the next expression that
matches the pattern from the given start number.
|
|
4
|
String group()
|
returns the matched subsequence.
|
|
5
|
int start()
|
returns the starting index of the
matched subsequence.
|
|
6
|
int end()
|
returns the ending index of the
matched subsequence.
|
|
7
|
int groupCount()
|
returns the total number of the
matched subsequence.
|
Pattern class
It is the compiled version of a regular expression. It is used to define a pattern for the regex engine.|
No.
|
Method
|
Description
|
|
1
|
static
Pattern compile(String regex)
|
compiles
the given regex and return the instance of pattern.
|
|
2
|
Matcher
matcher(CharSequence input)
|
creates a
matcher that matches the given input with pattern.
|
|
3
|
static
boolean matches(String regex, CharSequence input)
|
It works
as the combination of compile and matcher methods. It compiles the regular
expression and matches the given input with the pattern.
|
|
4
|
String[]
split(CharSequence input)
|
splits the
given input string around matches of given pattern.
|
|
5
|
String
pattern()
|
returns
the regex pattern.
|
Regex Character classes
|
No.
|
Character Class
|
Description
|
|
1
|
[abc]
|
a, b, or c
(simple class)
|
|
2
|
[^abc]
|
Any
character except a, b, or c (negation)
|
|
3
|
[a-zA-Z]
|
a through
z or A through Z, inclusive (range)
|
|
4
|
[a-d[m-p]]
|
a through
d, or m through p: [a-dm-p] (union)
|
|
5
|
[a-z&&[def]]
|
d, e, or f
(intersection)
|
|
6
|
[a-z&&[^bc]]
|
a through
z, except for b and c: [ad-z] (subtraction)
|
|
7
|
[a-z&&[^m-p]]
|
a through
z, and not m through p: [a-lq-z](subtraction)
|
Regex Metacharacters
The regular expression metacharacters work as a short codes.|
Regex
|
Description
|
|
.
|
Any
character (may or may not match terminator)
|
|
\d
|
Any
digits, short of [0-9]
|
|
\D
|
Any
non-digit, short for [^0-9]
|
|
\s
|
Any
whitespace character, short for [\t\n\x0B\f\r]
|
|
\S
|
Any
non-whitespace character, short for [^\s]
|
|
\w
|
Any word
character, short for [a-zA-Z_0-9]
|
|
\W
|
Any
non-word character, short for [^\w]
|
|
\b
|
A word
boundary
|
|
\B
|
A non word
boundary
|
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