Dart Basic syntax - string - Moment For Technology

3. Strings

3.1 string creation

1. String definition

Use single or double quotation marks

String a = "abcdefg";
String b = '12345';
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2. Create a multi-line string with built-in formatting

Use three single quotes or three double quotes to create a multi-line string with built-in formatting, such as newlines and indentation, and output whatever is written inside.

Three single quotes

String e = '''asd
     fdsd
       fff
    
    ''';
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Three double quotes

String f = """ 1
    2
    3
    4
    """;
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3, create raw string with r (special characters such as escape characters will be printed, not automatically escaped)

String str1=r'Hello \n  World'   
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3.2. Common string attributes

1. General attributes

String a20 = "aaaa";
String a21 = "";
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1. The length of the string

print(a20.length); / / 4Copy the code

2. Whether it is empty

print(a20.isEmpty); //false print(a21.isEmpty); //trueCopy the code

3, whether is not empty

print(a20.isNotEmpty); //true print(a21.isNotEmpty); //falseCopy the code

2. String concatenation

String a = "abcdefg";
String b = '12345';
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1. Use the + sign to connect

String c = a + b; Print (c); //abcdefg12345Copy the code

2, use adjacent space character concatenation, must be two strings cannot be variables

String d = 'aaa' 'bbb'; Print (d); print(d); //aaabbbCopy the code

String template, use ${} to embed a string variable/expression into another string

1, variables,

String a1 = "aa";
String b1 = "bb${a1}bb";
print(b1); //bbaabb
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2. Expressions

String a1 = "aa";
String b2 = "bb${a1.toUpperCase()}bb";
print(b2); //bbAAbb
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4. Conversion between strings and numbers

1, string to int value

int int1 = int.parse("33"); print(int1); / / 33Copy the code

2. String to double

Double d1 = double. Parse (" 3.33 "); print(d1); / / 3.33Copy the code

3. Value to string

print(33.toString()); Print (3.34. The toString ());Copy the code

4, the value of the string to retain precision

Print (3.12345 toStringAsFixed (3)); // Retain accuracy 3.123Copy the code

5. String cutting

String a2 = "aaabbb";
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1, including the head without the tail

print(a2.substring(0, 2)); //aa includes the head but not the tailCopy the code

2, from the specified index to the end

print(a2.substring(3)); // BBB from index to endCopy the code

3. Split returns an array

String a5 = "a,d,d d,c,,"; List<String> a6 = a5.split(","); Print (a6.length); print(a6.length); / / 6 print (a6); //[a, d, d d, c,];Copy the code

4, regular matching, split string

String strB = "abba";
print(strB.split(new RegExp(r"b*")));
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5. Query and replace

String a8 = "a b,c"; String a7 = a8.splitMapJoin(",",// Query ",", replace "with the return value of onMatch," replace other onmatches with the return value of onNonMatch: (Match Match) {return "a"; }, onNonMatch: (String nonMatch) { return "b"; }); print(a7); //bab a b,c => babCopy the code

6. Check whether the string contains or ends with XXX

String a3 = "aaabbbccc";
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1. Whether to start with ‘XXX’

print(a3.startsWith("aa")); //true print(a3.startsWith("aa", 3)); //false Start with index=3Copy the code

2, whether to end with ‘XXX’

print(a3.endsWith("c")); //true
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3. Whether to include ‘XXX’

print(a3.contains("ab")); //true
print(a3.contains("ac")); //false
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4. Whether to include ‘XXX’ from somewhere

print(a3.contains("ab", 3)); //false Start with index=3Copy the code

7. String replacement

String a4 = "abcdeab";
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Replace all of them

print(a4.replaceAll("ab","cc")); // replace all qualified cccdeccCopy the code

Replace only the first one that meets the criteria

print(a4.replaceFirst("ab", "dd")); //ddcdeab replaces only the first one that meets the conditionCopy the code

Replace the first one that meets the criteria starting at index=3

print(a4.replaceFirst("ab", "dd",3)); //abcdedd replaces the first qualified index with index=3Copy the code

Range of substitution from 0 to 3 including 0 without 3

print(a4.replaceRange(1, 3, "z")); // Replace the range from 0 to 3 with 0 but not 3Copy the code

Replaces the specified string with the method return value

Print (a4. ReplaceAllMapped ("c", (Match Match){//abyydeab replace the specified string with a method return value return "yy"; }));Copy the code

Replaces the specified string with the method return value starting with index=2

// abcDEA333 replace the specified string with the method return value from index=2 print(a4.replaceFirstMapped("b", (Match Match){return "333"; }, 2));Copy the code

8. String lookup

String a9 = "aababcc1bc23";
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Gets the position at which the specified character appears

String str = 'Dartisans';
print(str.indexOf('art'));
print(str.indexOf(new RegExp(r'[A-Z][a-z]')));
print(str.lastIndexOf('a'));
print(str.lastIndexOf(new RegExp(r'a(r|n)')));
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The first index that meets the criteria

print(a9.indexOf("ab")); / / 1Copy the code

Index =xx

print(a9.indexOf("ab",2)); Print (a9.indexof ("ab",4)); print(a9.indexof ("ab",4)); // index=4; // index=4Copy the code

Looking backwards returns the first index that matches the criteria

print(a9.lastIndexOf("bc")); //8 Returns the first index that matches the condition from back to frontCopy the code

Start with index= XXX and return -1 if no index is found

Print (a9.lastindexof (" BC ",3)); print(a9.lastindexof (" BC ",3));Copy the code

// start index=7 and return the first index that meets the condition

print(a9.lastIndexOf("bc",7));
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9. Remove whitespace

String a11 = " aab bcc "; print(a11); // aab bccCopy the code

Remove the left and right Spaces

print(a11.trim()); //aab BCC remove the left and right SpacesCopy the code

Remove the space on the right

print(a11.trimRight()); // aab BCC removes the right spaceCopy the code

Remove the left space

print(a11.trimLeft()); // aab BCC // remove left SpacesCopy the code

10. Replace the remaining bits of the completion length with the specified string

String a13 = "111";
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The remaining three bits are complemented by “” by default

print(a13.padLeft(6)); // the remaining three bits are completed by defaultCopy the code

The remaining three bits specify “c”

print(a13.padRight(6,"c")); // 111CCC specifies the remaining 3 bits to use "C"Copy the code

The remaining three bits each specify that the total length is not 6 when replaced with “dd”

print(a13.padRight(6,"dd")); // 111DDDDDD three bits each bit specifies that the total length is not 6 after "dd" is usedCopy the code

Returns the original string if the specified length is less than the original string length

print(a13.padLeft(2,"e")); //111 Returns the original string if the specified length is less than the original string lengthCopy the code

11. String sequence comparison

String a12 = "bbcc"; print(a12.compareTo("aaa")); B >a print(a12.compareTo(" BBCC ")); //0 print(a12.compareTo("dd")); //-1 b<d in ASCIICopy the code

12. Unicode encoding of strings

CodeUnitAt (method returns a 16-bit utf-16 codeUnitAt a given index)
- The index- argument represents the character index in the string.
- Return value Returns a numeric value.

String.codeUnitAt(int index)
void main() { 
   var res = "Good Day"; 
   print("Code Unit of index 0 (G): ${res.codeUnitAt(0)}");  
}
Code Unit of index 0 (G): 71
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CodeUnits (property returns a list of utf-16 codeUnits for the given string)

String.codeUnits
void main() { String str = "Hello"; print(str.codeUnits); }
 
[72, 101, 108, 108, 111]
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String operators (+, ==, [])

+ : add operator, string concatenation function

String a = 'abc'; String b = 'cbd'; print(a+b); //abccbdCopy the code

== : The equal operator that compares whether two strings are the same

String a = 'abc'; String b = '2'; if(a == b){ print('true'); }else{ print('false'); } / / returns falseCopy the code

[] : value operator that retrieves a single character pointed to by the string index bit

String a = 'abc'; String b = '2'; print(a[1]); //bCopy the code

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Dart Basic syntax – string

3. Strings

3.1 string creation

1. String definition

2. Create a multi-line string with built-in formatting

3, create raw string with r (special characters such as escape characters will be printed, not automatically escaped)

3.2. Common string attributes

1. General attributes

2. String concatenation

String template, use ${} to embed a string variable/expression into another string

4. Conversion between strings and numbers

5. String cutting

6. Check whether the string contains or ends with XXX

7. String replacement

8. String lookup

9. Remove whitespace

10. Replace the remaining bits of the completion length with the specified string

11. String sequence comparison

12. Unicode encoding of strings

String operators (+, ==, [])

Dart Basic syntax – string

3. Strings

3.1 string creation

1. String definition

2. Create a multi-line string with built-in formatting

3, create raw string with r (special characters such as escape characters will be printed, not automatically escaped)

3.2. Common string attributes

1. General attributes

2. String concatenation

String template, use ${} to embed a string variable/expression into another string

4. Conversion between strings and numbers

5. String cutting

6. Check whether the string contains or ends with XXX

7. String replacement

8. String lookup

9. Remove whitespace

10. Replace the remaining bits of the completion length with the specified string

11. String sequence comparison

12. Unicode encoding of strings

String operators (+, ==, [])

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