STRINGS

1
STRINGS

• Chapter 13

2
String class

• A String is a Class not a primitive
• Therefore, a String is a doughnut
• A String object has data
• A String object has methods

3
constructors

• A constructor is a method that is executed when
  an object is created
• The String class has multiple constructors
• String s1
• String s2 new String()
• String s3 new String(Buffalo)
• String s4 new String(s3)
• String s5 Bills
• String s6 s3 s5 are great

4
String methods

• Since a String is a class, a String object has
  methods
• To declare a String
• String s1 Buffalo
• To run a String method, you key the String object
  name, a . (period), and then the method name
• s1.charAt(3)

5
length()

• The length() method returns an int that contains
  the number of characters in the String.
• A String is not an array of characters terminated
  by a null (that is C)
• String s1 Buffalo
• int x s1.length() // x is 7
• String s2 Hi Mom and Dad!
• int x s2.length() // x is 15

6
charAt(int)

• charAt(int x) returns the character that is in
  the xth position of the String.
• Note the first character of a String is in
  position 0 (not 1)
• String s1 Buffalo)
• char ch s1.charAt(5) // ch is an l
• char ch s1.charAt(0) // ch is an B
• char ch s1.charAt(9) // error

7
equals(String)

• The equals method returns a true or false
• String s1 Buffalo
• String s2 Bills
• if(s1.equals(s2)) // returns false
• If(s1.equals(Buffalo) // returns true
• If(s1 s1) will probably return false
• You cannot use to compare Strings.
• compares the references to 2 Strings

8
toLowerCase() toUpperCase()

• toLowerCase() returns a copy of the String with
  all lower case
• toUpperCase() returns a copy of the String with
  all upper case
• String s1, s2, s3 Buffalo
• s1 s3.toLowerCase(s3) // buffalo
• s2 s3.toUpperCase(s3) // BUFFALO

9
substring()

• substring(int x, int y)
• Returns a substring from position x to one
  character before position y
• substring(int x)
• Returns a substring from position x to the end of
  the String
• String s1, s2 Buffalo
• s1 s2.substring(2,5) // returns ffa
• s1 s2.substring(4) // returns alo

10
parseInt(String)

• parseInt() is a method in the Integer class
• parseInt() converts a String into an int
• Int x
• String s1 123
• X Integer.parseInt(2) // x is 2
• X Integer.parseInt(s1) // x is 123
• X Integer.parseInt(ab) // error