Java Reference
In-Depth Information
1
// Fig. 20.7: Stack.java
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// Stack generic class declaration.
3
import
java.util.ArrayList;
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public class
Stack<T>
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{
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private final
ArrayList<T> elements;
// ArrayList stores stack elements
8
9
// no-argument constructor creates a stack of the default size
10
public
Stack()
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{
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this
(
10
);
// default stack size
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}
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// constructor creates a stack of the specified number of elements
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public
Stack(
int
capacity)
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{
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int
initCapacity = capacity >
0
? capacity :
10
;
// validate
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elements = new ArrayList<T>(initCapacity);
// create ArrayList
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}
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// push element onto stack
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public void
push(T pushValue)
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{
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elements.add(pushValue);
// place pushValue on Stack
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}
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// return the top element if not empty; else throw EmptyStackException
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public
T pop()
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{
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if
(elements.isEmpty())
// if stack is empty
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throw new
EmptyStackException(
"Stack is empty, cannot pop"
);
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// remove and return top element of Stack
35
return
elements.remove(elements.size() -
1
);
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}
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}
// end class Stack<T>
Fig. 20.7
|
Stack
generic class declaration.
Method
push
(lines 23-26) uses
ArrayList
method
add
to append the pushed item
to the end of the
ArrayList
elements
. The last element in the
ArrayList
represents the
top
of the stack.
Method
pop
(lines 29-36) first determines whether an attempt is being made to pop
an element from an empty
Stack
. If so, line 32 throws an
EmptyStackException
(declared
in Fig. 20.8). Otherwise, line 35 in Fig. 20.7 returns the top element of the
Stack
by
removing the last element in the underlying
ArrayList
.
Class
EmptyStackException
(Fig. 20.8) provides a no-argument constructor and a
one-argument constructor. The no-argument constructor sets the default error message,
and the one-argument constructor sets a custom error message.
As with generic methods, when a generic class is compiled, the compiler performs
era-
sure
on the class's type parameters and replaces them with their upper bounds. For class
