String

• String is an object
• String is immutable

Creating String

• String str = "Hello world!";
  • Point to an object in string pool
• Constructors
  • String(char [])
  • String(byte [])
  • String(String)
  • Point to an object in heap

Common String Methods

• int length()

• String toLowerCase()

• String toUpperCase()

• String trim()

• String substring(int begin)

• String substring(int begin, int end)

  • [begin, end)

• String replace(char old, char new)

• String replaceAll(String regex, String replacement)

• boolean startsWith(String s)

• boolean endsWith(String s)

• char charAt(int index)

• int indexOf(char c)

• int indexOf(String s)

• int lastIndexOf(char c)

• boolean equals(String s)

• boolean equalsIgnoreCase(String s)

• int compareTo(String s)

  • Compares two strings lexicographically

• boolean matches(String regex)

• String[] split(String regex, int limit)

• String[] split(String regex)

  • This method works as if by invoking the two-argument split method with the given expression and a limit argument of zero
  • Trailing empty strings will therefore be discarded

• static String String.join(CharSequence delimiter, CharSequence... elements)

• char[] toCharArray()

• static String String.valueOf(int i)

  • Convert other data type value to a string

Regualr Expression

regex-cheatsheet

StringBuffer & StringBuilder

• StringBuffer
  • "Mutable String"
  • append(), insert()
  • Initially will have a size of 16 capacity
  • It is thread-safe
• StringBuilder
  • Basically same as StringBuffer
  • It is not thread-safe, but faster
  • +, += is actually implemented by StringBuilder, one operator creates a new StringBuilder object

Printing

• // Only take one parameter
  System.out.print()
  System.out.println()
  
  // Formatted output
  System.out.printf()
  System.out.format()