Java Reference
In-Depth Information
o1.compareTo(o2)
⇒
Returns a positive integer if
o1
is bigger, 0 if they are equal,
and a negative number if
o1
is smaller.
o1.class
⇒
Returns the runtime type of
o1
.
Returns true if the runtime type of
o1
is the
C
class or one of
its direct or indirect subclasses.
⇒
o1 instanceof C
⇒
The
o1
object becomes a copy of the
o2
object.
o1 = o2.clone();
The
C
class contains a
compareTo
method that can be used to compare objects of type
C
.
{
...
}⇒
class C implements Comparable<C>
Collections.sort(a);
Sorts an
ArrayList
of
Comparable
objects. The
compareTo
method is used to compare the objects.
⇒
Sorts an array of
Comparable
objects. The
compareTo
method
is used to compare the objects.
⇒
Arrays.sort(a);
public int m()
{
...
}⇒
The
m
method is accessible everywhere.
int m()
{
...
}⇒
The
m
method is accessible only within the package.
protected int m()
{
The
m
method is accessible within the package and in
subclasses (direct or indirect).
...
}⇒
private int a;
⇒
The variable
a
is only accessible within the class. As a general
rule, define all non constant variables as
private
.
private int m()
{
...
}⇒
The
m
method is accessible within the class.
The
C
class is accessible from everywhere. Every Java file
must have exactly one
public
class that has exactly the same name as the name of
the file.
{
...
}⇒
public class C
{
...
}⇒
The
C
class is only accessible within the package.
class C
final int m()
{
...
}⇒
The
m
method cannot be overridden.
abstract void m();
Defines the
m
method as abstract. The method must be
overridden in the subclasses.
⇒
8.16 Important Points
1. Class composition and class inheritance are similar. However, there are few differences.
(a) They use different syntax.
(b) Every object in a subclass contains a reference to exactly one object of the
superclass that is not
null
. Conversely, an object can contain inside it 0 or more
non-null references to objects.
(c) Class composition does not support dynamic binding.
