Detail description about Java Array and Regex

Normally, array is a collection of similar type of elements that have contiguous memory location.rnJava 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.rnAdvantage of Java Arrayrn• 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 ArrayrnSize 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 core java training in Bangalorern• rnTypes of Array in javarnThere are two types of array. • Single Dimensional Arrayrn• Multidimensional Array rnSingle Dimensional ArrayrnOne 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 Arrayrn 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 java training institute bangalore Marathahalli rnJava RegexrnThe Java Regex or Regular Expression is an API to define pattern for searching or manipulating strings.rnIt 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.rnJava Regex API provides 1 interface and 3 classes in java.util.regex package.rnjava.util.regex packagernIt provides following classes and interface for regular expressions. The Matcher and Pattern classes are widely used in java regular expression.rn1. MatchResult interfacern2. Matcher classrn3. Pattern classrn4. PatternSyntaxException class Matcher classrnIt implements MatchResult interface. It is a regex engine i.e. used to perform match operations on a character sequence.rnNo. Method Descriptionrn1 boolean matches() test whether the regular expression matches the pattern.rn2 boolean find() finds the next expression that matches the pattern.rn3 boolean find(int start) finds the next expression that matches the pattern from the given start number.rn4 String group() returns the matched subsequence.rn5 int start() returns the starting index of the matched subsequence.rn6 int end() returns the ending index of the matched subsequence.rn7 int groupCount() returns the total number of the matched subsequence.rnPattern classrnIt is the compiled version of a regular expression. It is used to define a pattern for the regex engine.rnNo. Method Descriptionrn1 static Pattern compile(String regex) compiles the given regex and return the instance of pattern.rn2 Matcher matcher(CharSequence input) creates a matcher that matches the given input with pattern.rn3 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.rn4 String[] split(CharSequence input) splits the given input string around matches of given pattern. rn5 String pattern() returns the regex pattern.rnRegex Character classesrnNo. Character Class Descriptionrn1 [abc] a, b, or c (simple class)rn2 [^abc] Any character except a, b, or c (negation)rn3 [a-zA-Z] a through z or A through Z, inclusive (range)rn4 [a-d[m-p]] a through d, or m through p: [a-dm-p] (union)rn5 [a-z&&[def]] d, e, or f (intersection)rn6 [a-z&&[^bc]] a through z, except for b and c: [ad-z] (subtraction)rn7 [a-z&&[^m-p]] a through z, and not m through p: [a-lq-z](subtraction)rnRegex MetacharactersrnThe regular expression metacharacters work as a short codes.rnRegex Descriptionrn. 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 \x0B\f ] \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 boundaryrn\B A non word boundary