Strings

1
Strings

• A string is a sequence of characters that is
  treated as a single value. Strings are objects.
• We have been using strings all along. For
  example, to display text
• Every time you use a string, a string object
  is created automatically.
• String is a class in the java.lang package.

2
Explicit String Objects

• A declaration and object creation are needed for
  instances of the String class. For example,

We normally use shorthand notation (only for
Strings)
3
Explicit String Objects

• Blitititi out to reality StringVar.java
• Blitititi out to reality StringVar2.java
• Blitititi out to reality StringVar2.java

4
String variables are References - 1
Code
Both word1 and word2 are allocated memory (to
store references), but the objects themselves are
not yet created, so they both contain null.
L
word1
word2
L
State of Memory
5
String variables are References - 2
Code
One String object is created and assigned to
word1, so word1 contains the address of this
object.
word1
word2
L
State of Memory
6
String variables are References - 3
Code
Content of word1, which is an address, is
assigned to word2, making word2 refer to the same
object.
State of Memory

• Gadzook out to reality StringAlias.java

7
Concatenating Strings

• The operator can also concatenate strings.
• A new string object is created - the operands are
  not affected
• Gadzook out to reality StringCat.java

8
Command line Strings

• The formal arguments to the main method receive
  strings from the command line arguments.
• When running a program, supply command line
  arguments after the program name, e.g.,
• java MyJavaProgram cat 27 'Java is great!'
• has three command line arguments.
• Gadzook out to reality StringCat.java

9
Accessing Individual Elements

• Individual characters in a String accessed with
  the charAt method.

10
Determining the Size

• We determine the number of characters in a String
  with the length method.

Error because no object is created for str3, so
it is a null.

• Olipidoo out to reality StringVowels.java
• Olipidoo out to reality StringWords.java

11
Equality () vs. equalsCase 1
word1 and word2 point to the same object.
word1 word2
word1.equals( word2 )
12
Equality () vs. equalsCase 2
word1
word2
word1 and word2 point to different objects having
the same string.
word1 word2
word1.equals( word2 )
13
Equality () vs. equalsCase 3
word1
word2
word1 and word2 point to different objects with
different strings.
word1 word2
word1.equals( word2 )

• Quixote out to reality StringJavas.java

14
Other Useful String Operators
15
Strings and Methods

• Strings are reference variables, so (like arrays)
  formal parameters point to the actual parameter
  data
• Strings returned from methods point to the data
  created in the method
• Likidylik out to reality StringMethod.java

16
Strings are Immutable

• A String object is immutable, which means that
  once a String object is created, is cannot be
  changed.
• It is not possible to add, delete, or modify
  characters of a String object.
• The methods of the String class, such as
  toUpperCase and substring, do not modify the
  original string they return a new string.
• Java adopts this immutability restriction to
  implement an efficient memory allocation scheme
  for managing String objects.
• Oieeeeiooo out to reality StringImmut.java

17
StringBuffer

• Creating a new string from the old one will work
  for most cases, but sometimes manipulating the
  content of a string directly is more convenient.
• Manipulation means operations such as replacing a
  character, appending a string with another
  string, deleting a portion of a string, and so
  forth.
• Java has a StringBuffer class for this.
• StringBuffers are created from strings (no
  shorthand)
• Ay out to reality StringBufferX.java
• Ay out to reality StringBufferMake.java