Update java/08_stack/SampleBrowser.java

java/08_stack/SampleBrowser.java

@@ -0,0 +1,193 @@
+package algo.lesson08;
+
+/**
+ * 使用前后栈实现浏览器的前进后退。
+ * 
+ * @author chinalwb
+ */
+public class SampleBrowser {
+
+    public static void main(String[] args) {
+        SampleBrowser browser = new SampleBrowser();
+        browser.open("http://www.baidu.com");
+        browser.open("http://news.baidu.com/");
+        browser.open("http://news.baidu.com/ent");
+        browser.goBack();
+        browser.goBack();
+        browser.goForward();
+        browser.open("http://www.qq.com");
+        browser.goForward();
+        browser.goBack();
+        browser.goForward();
+        browser.goBack();
+        browser.goBack();
+        browser.goBack();
+        browser.goBack();
+        browser.checkCurrentPage();
+    }
+
+    private String currentPage;
+    private LinkedListBasedStack backStack;
+    private LinkedListBasedStack forwardStack;
+
+    public SampleBrowser() {
+        this.backStack = new LinkedListBasedStack();
+        this.forwardStack = new LinkedListBasedStack();
+    }
+
+    public void open(String url) {
+        if (this.currentPage != null) {
+            this.backStack.push(this.currentPage);
+            this.forwardStack.clear();
+        }
+        showUrl(url, "Open");
+    }
+
+    public boolean canGoBack() {
+        return this.backStack.size() > 0;
+    }
+
+    public boolean canGoForward() {
+        return this.forwardStack.size() > 0;
+    }
+
+    public String goBack() {
+        if (this.canGoBack()) {
+            this.forwardStack.push(this.currentPage);
+            String backUrl = this.backStack.pop();
+            showUrl(backUrl, "Back");
+            return backUrl;
+        }
+
+        System.out.println("* Cannot go back, no pages behind.");
+        return null;
+    }
+
+    public String goForward() {
+        if (this.canGoForward()) {
+            this.backStack.push(this.currentPage);
+            String forwardUrl = this.forwardStack.pop();
+            showUrl(forwardUrl, "Foward");
+            return forwardUrl;
+        }
+
+        System.out.println("** Cannot go forward, no pages ahead.");
+        return null;
+    }
+
+    public void showUrl(String url, String prefix) {
+        this.currentPage = url;
+        System.out.println(prefix + " page == " + url);
+    }
+
+    public void checkCurrentPage() {
+        System.out.println("Current page is: " + this.currentPage);
+    }
+
+    /**
+     * A LinkedList based Stack implementation.
+     */
+    public static class LinkedListBasedStack {
+
+//        public static void main(String[] args) {
+//            LinkedListBasedStack stack = new LinkedListBasedStack();
+//            stack.push("A");
+//            stack.push("B");
+//            stack.push("C");
+//            stack.pop();
+//            stack.push("D");
+//            stack.push("E");
+//            stack.pop();
+//            stack.push("F");
+//            stack.print();
+//
+////        String data = stack.getTopData();
+////        System.out.println("Top data == " + data);
+//        }
+
+        private int size;
+        private Node top;
+
+        static Node createNode(String data, Node next) {
+            return new Node(data, next);
+        }
+
+        public void clear() {
+            this.top = null;
+            this.size = 0;
+        }
+
+        public void push(String data) {
+            Node node = createNode(data, this.top);
+            this.top = node;
+            this.size++;
+        }
+
+        public String pop() {
+            Node popNode = this.top;
+            if (popNode == null) {
+                System.out.println("Stack is empty.");
+                return null;
+            }
+            this.top = popNode.next;
+            if (this.size > 0) {
+                this.size--;
+            }
+            return popNode.data;
+        }
+
+        public String getTopData() {
+            if (this.top == null) {
+                return null;
+            }
+            return this.top.data;
+        }
+
+        public int size() {
+            return this.size;
+        }
+
+        public void print() {
+            System.out.println("Print stack:");
+            Node currentNode = this.top;
+            while (currentNode != null) {
+                String data = currentNode.getData();
+                System.out.print(data + "\t");
+                currentNode = currentNode.next;
+            }
+            System.out.println();
+        }
+
+        public static class Node {
+
+            private String data;
+            private Node next;
+
+            public Node(String data) {
+                this(data, null);
+            }
+
+            public Node(String data, Node next) {
+                this.data = data;
+                this.next = next;
+            }
+
+            public void setData(String data) {
+                this.data = data;
+            }
+
+            public String getData() {
+                return this.data;
+            }
+
+            public void setNext(Node next) {
+                this.next = next;
+            }
+
+            public Node getNext() {
+                return this.next;
+            }
+        }
+
+    }
+}