Strings

Overview: 2.6.0

• Strings are objects of the String class
  • Hold sequence of characters
  • Class defines the data that that object has
• Classes begin with capital letter
  • Primitives start with a lower case letter

Null and Object References

• The keyword null indicates that a variable doesn’t reference any object yet
  • A reference is a way to find the actual object in memory
    • Like a contact in your phone

Constructing a String

• Two ways to construct a string
  • Using the new keyword and a class constructor
    • String myString = new String("Hello, world");
  • Create a string literal
    • A set of characters in double quotes
    • `String myString = “Hello, world”;
• Both ways create a String class, store the value in memory, and set myString to reference the new string

Packages and Inherence

• Full name for String is java.lang.String
  • java.lang is the package name
    • Every class is in a package
    • java.lang is used for standard packages
• Every object knows it’s class
• Every object knows it’s parent class
  • class can inherit object fields and methods from a parent
  • superclass is another word from parent
  • All classes inherit from java.lang.Object

String Operators - Concatenation: 2.6.1

• Strings can be appended to each other with + or +=
  • Called concatenation
  • Works with non-string values
    • these will be converted using toString
• Spaces are not added automatically
• Variables are never put inside quotes

Order of operations

• The same operators are processed left to right
  • "12" + 4 + 3 becomes "1243"
    • 4 becomes a string, then 3 does too
  • to print "127", use addition

Escape characters

• To print a literal double quote, you need to “escape” it with a backslash
  • double quote is a reserved character in Java
  • "\""
• To use a literal backslash, escape it with a bashslash
  • "\\"
• "\n" is a newline character

Summary: 2.6.3

• Strings are objects of the String class
  • Hold sequences of characters
  • Created with a string literal…
    • String s = "hello";
  • Or by calling the class constructor
    • String s = new String("Hello");
• new creates a new object of a class
• null indicates that an object reference doesn’t refer to anything
• Strings can be concatenated with + or +=
  • Primitives can be concatenated with Strings
    • causes implicit conversions of the values
• Escape sequences start with backslash (\) and have special meanings
  • This course covers \", \\, and \n to mean a literal doublequote, literal backslash, and newline character.