Making a stack from a LinkedList
A stack is sometimes referred to as a “last-in, first-out” (LIFO) container. That is, whatever you “push” on the stack last is the first item you can “pop” out. Like all of the other containers in Java, what you push and pop are Objects, so you must cast what you pop, unless you’re just using Object behavior.
The LinkedList has methods that directly implement stack functionality, so you can also just use a LinkedList rather than making a stack class. However, a stack class can sometimes tell the story better:
//: c11:StackL.java
// Making a stack from a LinkedList.
import com.bruceeckel.simpletest.*;
import java.util.*;
import com.bruceeckel.util.*;
public class StackL {
private static Test monitor = new Test();
private LinkedList list = new LinkedList();
public void push(Object v) { list.addFirst(v); }
public Object top() { return list.getFirst(); }
public Object pop() { return list.removeFirst(); }
public static void main(String[] args) {
StackL stack = new StackL();
for(int i = 0; i < 10; i++)
stack.push(Collections2.countries.next());
System.out.println(stack.top());
System.out.println(stack.top());
System.out.println(stack.pop());
System.out.println(stack.pop());
System.out.println(stack.pop());
monitor.expect(new String[] {
"CHAD",
"CHAD",
"CHAD",
"CENTRAL AFRICAN REPUBLIC",
"CAPE VERDE"
});
}
} ///:~
If you want only stack behavior, inheritance is inappropriate here because it would produce a class with all the rest of the LinkedList methods (you’ll see later that this very mistake was made by the Java 1.0 library designers with Stack).
