Java Reference
In-Depth Information
s.setCharAt(3,'a');
⇒
Changes the character at position 3 to
a
. The method can
'
'
only be applied to objects of type
StringBuffer
.
⇒
s.deleteCharAt(3);
Removes the character at position 3. The characters after
position 3 are shifted one position to the left. The method can only be applied to
objects of type
StringBuffer
.
⇒
Creates a new
StringBuffer
StringBuffer s = new StringBuffer("John");
object with text
John
.
s.append("Bob");
⇒
Appends
Bob
to the
StringBuffer
.
7.8 Important Points
1. The classes
Integer
,
Character
,
Double
,and
String
, among others, are immutable.
In other words, we cannot modify objects that belong to these classes. If we try to
do so, then new objects are created. As a consequence, if a method tries to modify a
formal parameter object that belongs to an immutable class, the changes will not be
seen by the calling method.
2. If we want to modify the characters of a
String
, then we need to create a
StringBuffer
object instead.
3. An
ArrayList
takes as input a type parameter. This parameter must be the name
of a class and cannot be the name of a primitive type (e.g.,
int
,
double
,or
char
).
To allow an
ArrayList
of primitive type, the wrapper classes
Byte
,
Short
,
Integer
,
Long
,
Float
,
Double
,
Character
,and
Boolean
are supported by Java.
4. If we want to associate a value with the constants of an
enum
type, then we need to
include a
private
constructor and a getter method.
5. Do not use the
set
method to add new values to an
ArrayList
. Instead, use the
add
method. The
set
method should be used to change existing values of an
ArrayList
.
6. The
size
method for an
ArrayList
returns the number of elements in the
ArrayList
.
This is different from the variable
length
for an array that returns the capacity of
the array. An
ArrayList
has no capacity. We can insert in it as many elements as we
want. The only restriction is the size of the available main memory.
7.9 Exercises
1. Write a method that takes in an
ArrayList
of doubles. The method should return the
second largest double in the
ArrayList
. You can assume that the
ArrayList
contains
at least two elements. The signature of the method should be as follows.
public static double
secondLargest(ArrayList
<
Double
>
a)
