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Stack
The concept of the stack was introduced earlier, with the LinkedList. What’s rather odd about the Java 1.0/1.1 Stack is that instead of using a Vector as a building block, Stack is inherited from Vector. So it has all of the characteristics and behaviors of a Vector plus some extra Stack behaviors. It’s difficult to know whether the designers consciously thought that this was an especially useful way of doing things, or whether it was just a naïve design; in any event it was clearly not reviewed before it was rushed into distribution, so this bad design is still hanging around (but you should never use it).
Here’s a simple demonstration of Stack that pushes each line from a String array:
//: c11:Stacks.java
// Demonstration of Stack Class.
import com.bruceeckel.simpletest.*;
import java.util.*;
import c08.Month;
public class Stacks {
private static Test monitor = new Test();
public static void main(String[] args) {
Stack stack = new Stack();
for(int i = 0; i < Month.month.length; i++)
stack.push(Month.month[i] + " ");
System.out.println("stack = " + stack);
// Treating a stack as a Vector:
stack.addElement("The last line");
System.out.println("element 5 = " +
stack.elementAt(5));
System.out.println("popping elements:");
while(!stack.empty())
System.out.println(stack.pop());
monitor.expect(new String[] {
"stack = [January , February , March , April , May "+
", June , July , August , September , October , " +
"November , December ]",
"element 5 = June ",
"popping elements:",
"The last line",
"December ",
"November ",
"October ",
"September ",
"August ",
"July ",
"June ",
"May ",
"April ",
"March ",
"February ",
"January "
});
}
} ///:~
Each line in the months array is inserted into the Stack with push( ), and later fetched from the top of the stack with a pop( ). To make a point, Vector operations are also performed on the Stack object. This is possible because, by virtue of inheritance, a Stack is a Vector. Thus, all operations that can be performed on a Vector can also be performed on a Stack, such as elementAt( ).
As mentioned earlier, you should use a LinkedList when you want stack behavior.
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