collections - Stack example

The Stack class represents a last-in-first-out (LIFO) stack of objects.

When a stack is first created, it contains no items.

A more complete and consistent set of LIFO stack operations is provided by the Deque interface and its implementations, which should be used in preference to this class. For example:

   
   Deque<Integer> stack = new ArrayDeque<Integer>(); // ArrayDeque since Java 1.6

If we want only stack behavior, inheritance is inappropriate in java because that would produce a class with all the rest of the ArrayDeque methods. Using composition, we choose which methods to expose and how to name them.

java.util.Stack is a bad desgin. It is extended java.util.Vector<E>.

case 1:

// onjava/Stack.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// A Stack class built with an ArrayDeque
package onjava;

import java.util.ArrayDeque;
import java.util.Deque;

public class Stack<T> {
  private Deque<T> storage = new ArrayDeque<>();

  public void push(T v) {
    storage.push(v);
  }

  public T peek() {
    return storage.peek();
  }

  public T pop() {
    return storage.pop();
  }

  public boolean isEmpty() {
    return storage.isEmpty();
  }

  @Override
  public String toString() {
    return storage.toString();
  }
}

The peek() method provides us with the top element without removing it from the top of the stack, while pop() removes and returns the top element.

case 2:

// collections/StackTest2.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

import onjava.*;

public class StackTest2 {
  public static void main(String[] args) {
    Stack<String> stack = new Stack<>(); // use case 1 class Stack
    for (String s : "My dog has fleas".split(" ")) {
      stack.push(s);
    }
    while (!stack.isEmpty()) {
      System.out.print(stack.pop() + " ");
    }
  }
}
/* Output:
fleas has dog My
*/

case 3:

// collections/StackCollision.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

public class StackCollision {
  public static void main(String[] args) {
    onjava.Stack<String> stack = new onjava.Stack<>();
    for (String s : "My dog has fleas".split(" ")) {
      stack.push(s);
    }
    while (!stack.isEmpty()) {
      System.out.print(stack.pop() + " ");
    }
    System.out.println();

    java.util.Stack<String> stack2 = new java.util.Stack<>();
    for (String s : "My dog has fleas".split(" ")) {
      stack2.push(s);
    }
    while (!stack2.empty()) {
      System.out.print(stack2.pop() + " ");
    }
  }
}
/* Output:
fleas has dog My
fleas has dog My
*/

references:

1. On Java 8 - Bruce Eckel

2. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/onjava/Stack.java

3. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/collections/StackTest2.java

4. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/collections/StackCollision.java

5. http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/util/Stack.java

6. https://docs.oracle.com/javase/8/docs/api/java/util/Stack.html

collections - Stack example

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