String_Class

String Class In Dart Programming Language

• is a part of dart:core.

• is an abstract class.

• implement Comparable,Pattern.

• String Literal

  String mystr= "my string bet. double quotes";//double quote literal
  mystr = 'my string bet. single quotes.'//single quote literal

• implements Comparable,Pattern

• You can use $ to interpolate the value of Dart expressions within strings.

  Example :

  var mystr = "Hello ${12/4}";//if single back slash'\' is showning before $ ignore it
  //it will be due Readme formating    
  print(mystr);
  /*Output :
  Hello 3
  */

• multiline string literal. Example :

  String s= """multi line 
            string
             in dart""";
  s = ''' multi line string using
  single quotes
  he
  ''';

• Concatenation in String Using '+' Opeartor

  Example :

  var myStr ="first string"+" second string"+"third string";
  print(myStr);
  /*Output:
  first string second stringthird string
  */  

Remarks

• You can access the string's singular element/character using following syntax :

  mystr[i];//i be the index of element between 0(the first index) and length of string

  Example:

  myStr = "Hello String";
  print("myStr[0] : "+myStr[0]);
  print("myStr[3] : "+myStr[3]);
  print("myStr[6] : "+myStr[6]);
  print("myStr[8] : "+myStr[8]);
  /*Output
  myStr[0] : H
  myStr[3] : l
  myStr[6] : S
  myStr[8] : r
  */  

• String in dart are immutable. Example:

  var str = "Hello";
  print(str[0]);//prints H
  str[0]= 'k';//Error :Try correcting the operator to an existing operator, or defining a '[]=' operator.

• A string is represented by a sequence of Unicode UTF-16 code units accessible through the [codeUnitAt] or the [codeUnits] members:

   string = 'Dart';
   string.codeUnitAt(0); // 68
   string.codeUnits;     // [68, 97, 114, 116]

Properties

• length :

  get length of string

  print("hiThisIsAString".length);//15

• hashCode :

  get hasCode derived from code unit of string.

  print("hashCode Prop 1 :"+"himySTr".hashCode.toString());
  print("hashCode Prop 2 :"+"himySTr23".hashCode.toString());

• isEmpty :

return true if string is empty ,false otherwise.

```dart
print("isEmpty 1: "+"".isEmpty.toString());//true
print("isEmpty 2: "+" ".isEmpty.toString());//false
print("isEmpty 3: "+"Hi String".isEmpty.toString());//false
```

• isNotEmpty :

return true if string is not empty ,false otherwise.

• Note :

You can't set these properties.

"histr".length =4;
//main.dart:63:11: Error: The setter 'length' isn't defined for the class 'String'.  

Important Methods

1. stringObj.toUpperCase()

: return an uppercase string comparable to original string.

Return Type: String

 print("UpperCase 1: "+"mystr".toUpperCase());
 print("UpperCase 2: "+"Hishds sdkjskd32".toUpperCase());
 /*Ouput:
 * UpperCase 1: MYSTR
 * UpperCase 2: HISHDS SDKJSKD32
 * */

2. stringObj.toLowerCase()

: return a lower case string comparable to original string. Return Type: String

print("LowerCase 1:"+"MY StriNg heRe".toLowerCase());
//LowerCase 1:my string here

3. stringObj.toCompare()

 * Compares this string to [other].
*
* Returns a negative value if `this` is ordered before `other`,
* a positive value if `this` is ordered after `other`,
* or zero if `this` and `other` are equivalent.
*
* The ordering is the same as the ordering of the code points at the first
* position where the two strings differ.
* If one string is a prefix of the other,
* then the shorter string is ordered before the longer string.
* If the strings have exactly the same content, they are equivalent with
* regard to the ordering.
* Ordering does not check for Unicode equivalence.
* The comparison is case sensitive.

Return Type: int

Example:

  print("Compare 1: "+ "this String".compareTo("other string").toString());
  print("Compare 2: "+ "this String".compareTo("this String").toString());
  print("Compare 3: "+ "this String".compareTo("thisstring").toString());
  print("Compare 4: "+"Z".compareTo('A').toString());
  print("Compare 5: "+'a'.compareTo('A').toString());
  print("Compare 6: "+'A'.compareTo('Z').toString());
  /*Output:
  Compare 1: 1
  Compare 2: 0
  Compare 3: -1
  Compare 4: 1
  Compare 5: 1
  Compare 6: -1
  */ 

4. stringObj.indexOf(String pattern,int start) :

used to find the starting index of given string inside stringObject which matches the pattern.

Return Type: int

  print("Index Of 1: \"hi i hate to use regex\".indexOf(\"hate\") : "+ "hi i hate to use regex".indexOf("hate").toString());
  print("Index Of 2: \"hi i hate to use use regex\".indexOf(\"use\"): "+ "hi i hate to use use regex".indexOf("use").toString());
  print("Index Of 3: \"hi i hate to use use use regex\".indexOf(\"use\"): "+ "hi i hate to use use use regex".indexOf("use").toString());
  print("Index Of 4: "+ "hi i hate to  regex\".indexOf(\"use\") : "+ "hi i hate to  regex".indexOf("use").toString());
  print("Index Of 5: \"hi i hate touse regex\".indexOf(\"use\") : "+ "hi i hate touse regex".indexOf("use").toString());
  //Note : pattern here isn't a pattern obj or regex
  print("Index Of 6: \"hi i hate touse use regex\".indexOf(\"\\suse\"): "+ "hi i hate touse use regex".indexOf("\\suse").toString());
  print("Index Of 7: : "+ "hi i hate to use use986 regex".indexOf("\\suse\\s").toString());
  //using **start** argument
  print("Index Of : : "+ "hi i hate to use use regex".indexOf("use",14).toString());
  // print("Index Of : : "+ "hi i hate to use use regex".indexOf("use",-3).toString());
  //RangeError (start): Invalid value: Not in inclusive range 0..26: -3
 /*Output :
 * Index Of 1: "hi i hate to use regex".indexOf("hate") : 5
  Index Of 2: "hi i hate to use use regex".indexOf("use"): 13
  Index Of 3: "hi i hate to use use use regex".indexOf("use"): 13
  Index Of 4: hi i hate to  regex".indexOf("use") : -1
  Index Of 5: "hi i hate touse regex".indexOf("use") : 12
  Index Of 6: "hi i hate touse use regex".indexOf("\suse"): -1
  Index Of 7: : -1
  Index Of : : 17
 * */

5. stringObj.substring(int start,int end)

: returns substring of str-object from start index to end index -1.

Return Type : string

//substring(start[,end])
//setting start only
print("substring 1: : "+ "1234567890AString Containing Numerical Characters".substring(10));
print("substring 2: : "+ "1234567890AString Containing Numerical Characters".substring(20));
print("substring 3: :"+ "1234567890AString Containing Numerical Characters".substring(10,20));
// print("substring 4: :"+ "1234567890AString Containing Numerical Characters".substring(20,10));
//Error : Unhandled exception:
// RangeError: Value not in range: 20
print("substring 5: : "+ "hi its there".substring(2,8));
/*Ouput:
* substring 1: "1234567890AString Containing Numerical Characters".substring(10) : AString Containing Numerical Characters
substring 2: "1234567890AString Containing Numerical Characters".substring(10) : ntaining Numerical Characters
substring 3: "1234567890AString Containing Numerical Characters".substring(10) :AString Co
substring 5: "hi its there".substring(2,8):  its t
* */

6. stringObj.replaceAll(Pattern form,String replace)

: returns a string which replaces all matches of form found in String Object with replace string.

Return Type : string

//replace(pattern,replace)
 //pattern - dtype Pattern
 //replace - dtype String
 print("replaceAll 1 : : "+"hi hi hi hi".replaceAll("hi","hey"));
 print("replaceAll 2 : : "+ "hi di gi ri".replaceAll(RegExp('[a-z]i'),"ho"));
 print("replaceAll 3 : : "+"hi gi di ri".replaceAll(" ","-"));
 print("replaceAll 4 : : "+"hi gi di ri".replaceAll("","-"));
/*Ouput:
* replaceAll 1 : : hey hey hey hey
 replaceAll 2 : : ho ho ho ho  
 replaceAll 3 : : hi-gi-di-ri
 replaceAll 4 : : -h-i- -g-i- -d-i- -r-i-
* */