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Regular Expression in java

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)

X?  X, once or not at all
X*  X, zero or more times
X+  X, one or more times
X{n}    X, exactly n times
X{n,}   X, at least n times
X{n,m}  X, at least n but not more than m times

Reluctant quantifiers
X?? X, once or not at all
X*? X, zero or more times
X+? X, one or more times
X{n}?   X, exactly n times
X{n,}?  X, at least n times
X{n,m}? X, at least n but not more than m times

Possessive quantifiers
X?+ X, once or not at all
X*+ X, zero or more times
X++ X, one or more times
X{n}+   X, exactly n times
X{n,}+  X, at least n times
X{n,m}+ X, at least n but not more than m times

To Split the String with spaces

String[] words = line.split("\\s+");


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Compress a String


public class StringCompression {

public StringCompression() {
// TODO Auto-generated constructor stub

public static void main(String[] args) {

public static String compressString(String str) {
//String str = "aaaabbbbbcccc";
char[] charArray = str.toCharArray();
String compressedString = "";
int i = 0;
while (i < charArray.length) { int counter = 1; int j = i + 1; while (j < charArray.length && charArray[i] == charArray[j]) { counter++; j++; i++; } compressedString = compressedString + charArray[i] + counter; i++; } //System.out.println(compressedString); String output =(compressedString.length() > charArray.length)? str: compressedString;
return output;