String Formatting and Regular Expressions

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What we’ll cover

Formatting Strings
Formatting System OutputStream
Formatter Class
Regular expressions

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Formatting Strings

Built-in Formatting Utilities

String.format()
System.out.format()
Formatter()

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Formatting: String Formatting

String formatting converts the value of objects to strings based on formats specified, then inserts them into another string.

Format specifiers

Format specifiers are flags which notify the compiler to insert values into a String.
- always preceded by a %
Specifier syntax
- %[argument_index$][flags][width][.precision]conversion

Formatting: String Formatting
Example 1

Formatting String arguments using %s specifier
- %s specifies a String value.

public void demo() {
  String formattedString = "Hey! [ %s ] is my name!";
  String arg1 = "John";
  String outputString = String.format(formattedString, arg1);
  System.out.println(outputString);
}

Output

Hey! [ John ] is my name!

Formatting: String Formatting
Example 2

Formatting Integer arguments using %d specifier
- %d specifies an integer value

public void demo() {
  String formattedString = "I am %d years old.";
  Integer arg1 = 25;
  String outputString = String.format(formattedString, arg1);
  System.out.println(outputString);
}

Output

I am 25 years old.

Formatting: String Formatting
Example

Formatting Double arguments using %f specifier
- %f specifies a decimal value
- . precedes positive integer value denoting precision of floating point value. (decimal precision)
- the integer value specifies the decimal precision of the double to formatted.

public void demo() {
  String formattedString = "I've finished %.5f percent of homework";
  Double arg1 = 79.87654321;
  String outputString = String.format(formattedString, arg1);
  System.out.println(outputString);
}

Output

I've finished 79.87654 percent of homework

Formatting: String Formatting
Example

Specifying precision of 3 decimal places.

public void demo() {
  String formattedString = "I've finished %.3f percent of homework";
  Double arg1 = 79.87654321;
  String outputString = String.format(formattedString, arg1);
  System.out.println(outputString);
}

Output

I've finished 79.876 percent of homework

Formatting: String Formatting
Example

Specifying precision of 2 decimal places.

public void demo() {
  String formattedString = "I've finished %.2f percent of homework";
  Double arg1 = 79.87654321;
  String outputString = String.format(formattedString, arg1);
  System.out.println(outputString);
}

Output

I've finished 79.87 percent of homework

Formatting: String Formatting
Example

public void demo() {
  Integer precision1 = 4;
  Integer precision2 = 5;
  Double valueToFormat = 79.87654321;
  String output1 = getHomeworkDetails(precision1, valueToFormat);
  String output2 = getHomeworkDetails(precision2, valueToFormat);
  System.out.println(output1);
  System.out.println(output2);
}

public String getHomeworkDetails(Integer decimalPrecision, Double valueToFormat) {
  String formattedString = new StringBuilder("I've finished %.")
    .append(decimalPrecision)
    .append("f percent of homework")
    .toString();
  return String.format(formattedString, valueToFormat);
}

Output

I've finished 79.8765 percent of homework
I've finished 79.87654 percent of homework

Formatting: String Formatting
Example

Formatting Character arguments using %c specifier
- %c specifies a character value

public void demo() {
  String formattedString = "My first initial is %c.";
  Character arg1 = 'J';
  String outputString = String.format(formattedString, arg1);
  System.out.println(outputString);
}

Output

My first initial is J.

Formatting: String Formatting
Example

Formatting String and Integer arguments
- Arguments are entered in the order they are specified

public void demo() {
  String formattedString = "Hey! My name is %s. I am %d years old.";
  String arg1 = "John";
  Integer arg2 = 25;
  String outputString = String.format(formattedString, arg1, arg2);
  System.out.println(outputString);
}

Output

Hey! My name is John. I am 25 years old.

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Formatting: System OutputStream

OutputStream formatting does not return a String value. Rather, it prints a formatted String to the console.

Formatting: System OutputStream
Example 1

Formatting String arguments using %s specifier

public void demo() {
  String formattedString = "Hey! [ %s ] is my name!";
  String arg1 = "John";
  System.out.format(formattedString, arg1);
}

Output

Hey! [ John ] is my name!

Formatting: System OutputStream
Example 2

Formatting Integer arguments using %d specifier

public void demo() {
  String formattedString = "I am %d years old.";
  Integer arg1 = 25;
  System.out.format(formattedString, arg1);
}

Output

I am 25 years old.

Formatting: System OutputStream
Example 3

Formatting String and Integer arguments

public void demo() {
  String formattedString = "Hey! My name is %s. I am %d years old.";
  String arg1 = "John";
  Integer arg2 = 25;
  System.out.format(formattedString, arg1, arg2);
}

Output

Hey! My name is John. I am 25 years old.

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Formatting: Formatter Class

used to format and output data to a specific destination, such as a string or a file output stream.

Formatting: Formatter
Example 1

Formatting String arguments

public void demo() {
  String fileName = "MyFile.txt";
  String formattedString = "Hi, my name is %s!";
  String arg1 = "John";

  FileOutputStream outputStream = new FileOutputStream(fileName);
  Formatter formatter = new Formatter(outputStream);
  formatter.format(formattedString, arg1);
  formatter.flush();
}

Output: MyFile.txt content

Hi, my name is John!

Formatting: Formatter
Example 2

Formatting Integer arguments

public void demo() {
  String fileName = "MyFile.txt";
  String formattedString = "Hi, my age is %d!";
  Integer arg1 = 25;

  FileOutputStream outputStream = new FileOutputStream(fileName);
  Formatter formatter = new Formatter(outputStream);
  formatter.format(formattedString, arg1);
  formatter.flush();
}

Output: MyFile.txt content

Hi, my age is 25!

Formatting: Formatter
Example 3

Formatting Double arguments

public void demo() {
  String fileName = "MyFile.txt";
  String formattedString = "Hi, my age is %.1f!";
  Double arg1 = 25.2;

  FileOutputStream outputStream = new FileOutputStream(fileName);
  Formatter formatter = new Formatter(outputStream);
  formatter.format(formattedString, arg1);
  formatter.flush();
}

Output: MyFile.txt content

Hi, my age is 25.2!

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##Reminder re: FileOutputStream When using FileOutputStream, you will need to either add a FileNotFoundException or use a try/catch block

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Regular expressions

are a sequence of symbols and characters expressing a string or pattern to be searched for within a longer piece of text.

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Character classes

| Expression | Description | |—————————————|————————————————| | . | any character except newline | \w, \d, \s | word / digit / whitespace | \W, \D, \S | not word / not digit / not whitespace | [abc] | any of a, b, or c | [^abc] | not a, not b, not c | [a-g] | character between a and g

Using Character Classes

Example 1 - Matching all characters

public void demo() {
    String text = "The Quick Brown Fox";
    String patternString = ".";
    Pattern pattern = Pattern.compile(patternString);
    Matcher matcher = pattern.matcher(text);
    for (int i = 0; matcher.find(); i++) {
        System.out.println(new StringBuilder()
                .append("\n-------------------")
                .append("\nValue = " + matcher.group())
                .append("\nMatch Number = " + i)
                .append("\nStarting index = " + matcher.start())
                .append("\nEnding index = " + matcher.end())
                .toString());

    }
}

Using Character Classes

Example 1 output

Value = T
Match Number = 0
Starting index = 0
Ending index = 1

-------------------
Value = h
Match Number = 1
Starting index = 1
Ending index = 2

-------------------
Value = e
Match Number = 2
Starting index = 2
Ending index = 3

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Anchors

| Expression | Description | |—————————————|————————————————| | ^abc$ | start / end of the string | \b, \B | word, digit, whitespace

Using Anchors

Example 1 - Fetch text from beginning of string

public void demo() {
    String text = "The Quick Brown";
    String patternString = "^The";
    Pattern pattern = Pattern.compile(patternString);
    Matcher matcher = pattern.matcher(text);
    for (int i = 0; matcher.find(); i++) {
        System.out.println(new StringBuilder()
                .append("\n-------------------")
                .append("\nValue = " + matcher.group())
                .append("\nMatch Number = " + i)
                .append("\nStarting index = " + matcher.start())
                .append("\nEnding index = " + matcher.end())
                .toString());
    }
}

Using Anchors

Example 1 output

-------------------
Value = The
Match Number = 0
Starting index = 0
Ending index = 3

Using Anchors

Example 2 - Fetch text from beginning of string

public void demo() {
    String text = "The Quick Brown";
    String patternString = "^Brown";
    Pattern pattern = Pattern.compile(patternString);
    Matcher matcher = pattern.matcher(text);
    for (int i = 0; matcher.find(); i++) {
        System.out.println(new StringBuilder()
                .append("\n-------------------")
                .append("\nValue = " + matcher.group())
                .append("\nMatch Number = " + i)
                .append("\nStarting index = " + matcher.start())
                .append("\nEnding index = " + matcher.end())
                .toString());
    }
}

Using Anchors

Example 2 output - Empty output; no matches

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Escaped characters

| Expression | Description | |—————————————|————————————————| | (abc) | capture group | \1 | backreference to group #1 | (?:abc) | non-capturing group | (?=abc) | positive lookahead | (?!abc) | negative lookahead

Using Escaped Characters

Example 1

public void demo() {
    String text = "The Quick Brown";
    String patternString = "(Brown)";
    Pattern pattern = Pattern.compile(patternString);
    Matcher matcher = pattern.matcher(text);
    for (int i = 0; matcher.find(); i++) {
        System.out.println(new StringBuilder()
                .append("\n-------------------")
                .append("\nValue = " + matcher.group())
                .append("\nMatch Number = " + i)
                .append("\nStarting index = " + matcher.start())
                .append("\nEnding index = " + matcher.end())
                .toString());
    }
}

Using Escaped Characters

Example 1 output

-------------------
Value = Brown
Match Number = 0
Starting index = 10
Ending index = 15

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Quantifies and Alternation

| Expression | Description | |—————————————|————————————————| | a*, a+, a? | 0 or more, 1 or more, 0 or 1 | a{5}, a{2, } | exactly five, two or more | a{1,3} | between one & three | a+? a{2,}? | match as few as possible

Using Quantifies and Alternation

Example 2 - Matching all words

public void demo() {
    String text = "The Quick Brown";
    String patternString = "\\w+";
    Pattern pattern = Pattern.compile(patternString);
    Matcher matcher = pattern.matcher(text);
    for (int i = 0; matcher.find(); i++) {
        System.out.println(new StringBuilder()
                .append("\n-------------------")
                .append("\nValue = " + matcher.group())
                .append("\nMatch Number = " + i)
                .append("\nStarting index = " + matcher.start())
                .append("\nEnding index = " + matcher.end())
                .toString());
    }
}

Using Quantifies and Alternation

Example 2 output

Value = The
Match Number = 0
Starting index = 0
Ending index = 3

-------------------
Value = Quick
Match Number = 1
Starting index = 4
Ending index = 9

-------------------
Value = Brown
Match Number = 2
Starting index = 10
Ending index = 15

More about regex symbols

a, b, c - match “a”, “b”, “c” respectively
. - matches any one character
* - match 0 or more occurrences of the last symbol
+ - match 1 or more occurrences of the last symbol
? - match 0 or 1 occurrences of the last symbol

String Formatting and Regular Expressions

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What we’ll cover

Formatting Strings

Built-in Formatting Utilities

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Formatting: String Formatting

Format specifiers

Formatting: String FormattingExample 1

Formatting: String FormattingExample 2

Formatting: String FormattingExample

Formatting: String FormattingExample

Formatting: String FormattingExample

Formatting: String FormattingExample

Formatting: String FormattingExample

Formatting: String FormattingExample

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Formatting: System OutputStream

Formatting: System OutputStreamExample 1

Formatting: System OutputStreamExample 2

Formatting: System OutputStreamExample 3

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Formatting: Formatter Class

Formatting: FormatterExample 1

Formatting: FormatterExample 2

Formatting: FormatterExample 3

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Regular expressions

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Character classes

Using Character Classes

Using Character Classes

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Anchors

Using Anchors

Using Anchors

Using Anchors

Using Anchors

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Escaped characters

Using Escaped Characters

Using Escaped Characters

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Quantifies and Alternation

Using Quantifies and Alternation

Using Quantifies and Alternation

More about regex symbols

More regex examples

Site for testing regex

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Formatting: String Formatting
Example 1

Formatting: String Formatting
Example 2

Formatting: String Formatting
Example

Formatting: String Formatting
Example

Formatting: String Formatting
Example

Formatting: String Formatting
Example

Formatting: String Formatting
Example

Formatting: String Formatting
Example

Formatting: System OutputStream
Example 1

Formatting: System OutputStream
Example 2

Formatting: System OutputStream
Example 3

Formatting: Formatter
Example 1

Formatting: Formatter
Example 2

Formatting: Formatter
Example 3