20162321王彪 2017-2018《程序设计与数据结构》第五周学习总结

学习目标

• 掌握Java Collections API的基本结构
• 理解Collection的抽象设计
• 掌握Collection实现的Java相关技术：继承/多态/泛型/接口
• 掌握栈的应用
• 掌握栈的实现（数组，链式）
• 分析Java Stack API

知识点总结

• 集合(collection)：线性的和非线性的；线性集合(linear collection)是集合中的元素排成一行。非线性集合是按不同于一行的方式来组织元素，例如按层次或是按网络的方式。
• 抽象(abstraction)在某些时候隐藏其细节。抽象数据类型(abstract data type,ADT)是其值和操作都没有在程序设计语言中定义的一种数据类型。它是抽象的，因为实现细节必须要定义，而且要对用户隐藏。

代码实现

• 用数组实现栈

public class ArrayStack<T> {
    private final int DEFAULT_CAPACITY = 10;
    private int count;
    private T[] stack;
    private T item;
    public T pop () {
        if (count==0){
            System.out.println("Wrong num");
        }
        else {
            item = stack[count-1];
            stack[count-1]=null;
        }
        return item;
    }
    public T peek(){
        if (count==0){
            System.out.println("Wrong num");
        }
        else {
            item = stack[count-1];
        }
        return item;
    }
    public boolean isEmpty(){
        if (count==0)
            return true;
        else
            return false;
    }
    public int size(){
        return count;
    }
    public ArrayStack(){
        count=0;
        stack =(T[])(new Object[DEFAULT_CAPACITY]);
    }
    public void push(T element){
        if (count==stack.length)
            expandCapacity();
        stack[count]=element;
        count++;
    }
    public String toString(){
        String result = "<top of stack>";
        for (int index=count-1;index>=0;index--)
            result += stack[index]+"
";
        return result+"<bottom of stack>";
    }
    private void expandCapacity(){
        T[] larger = (T[])(new Object[stack.length*2]);
        for (int index=0;index<stack.length;index++){
            larger[index] = stack[index];
        }
        stack = larger;
    }

• peek()操作要注意当前栈是否是空。

• 用链表实现栈

public class LinkedStack<T> implements Stack<T>
{
    private int count;
    private LinearNode<T> top = new LinearNode<T>(null);//表头,数据为空
    private LinearNode<T> end = new LinearNode<T>(null);//表尾

    //----------------------------------------------------------------
    //  Creates an empty stack using the default capacity.
    // ----------------------------------------------------------------
    public LinkedStack() {
        top.setNext(end);
        count=0;
    }
//----------------------------------------------------------------
//  Removes the element at the top of this stack and returns a
//  reference to it. Throws an EmptyCollectionException if the
//  stack contains no elements.
// ----------------------------------------------------------------
public T pop() throws EmptyCollectionException {
        if (count == 0) throw new EmptyCollectionException ("Pop operation failed. " + "The stack is empty.");
    T result = top.getNext().getElement();
    top.setNext(top.getNext().getNext());
    top.setElement(null);

    count--;
return result;
}
//----------------------------------------------------------------
    //   Returns a string representation of this stack.
// ----------------------------------------------------------------
    public String toString() {
        String result = "<top of stack>
";
        LinearNode current = top;
        while (current != null) {
            result += current.getElement() + "
";
            current = current.getNext();
        }
        return result + "<bottom of stack>";
    }
    //----------------------------------------------------------------
//  The following methods are left as programming projects.
// ----------------------------------------------------------------

    @Override
    public int hashCode() {
        return super.hashCode();
    }
    @Override
    public void push(T element) {
            LinearNode<T> now = new LinearNode<T>(element);//now是用来保存加入元素的节点类的实例
            now.setNext(top.getNext());//指向top指向的对象
            top.setNext(now);
            count++;
    }
    @Override
    public T peek() {
        return top.getNext().getElement();
    }
    @Override
    public boolean isEmpty() {
        if (count==0)
            return true;
        else
            return false;
    }

    @Override
    public int size() {
        return count;
    }
    public static void main(String[] args) {
        LinkedStack mLinked = new LinkedStack();
        mLinked.push(1);
        System.out.println(mLinked.isEmpty());
    }
    }
//************************************************************
//  LinearNode.java       Java Foundations
// //  Represents a node in a linked list.
// ************************************************************
       class LinearNode<T> {
        private LinearNode<T> next;
        private T element;
//----------------------------------------------------------------
//  Creates an empty node.
// ----------------------------------------------------------------
public LinearNode() {
        next = null;
        element = null; }
//----------------------------------------------------------------
//  Creates a node storing the specified element.
// ---------------------------------------------------------------
public LinearNode (T elem) {
        next = null;
        element = elem; }
//----------------------------------------------------------------
//  Returns the node that follows this one.
// ----------------------------------------------------------------
public LinearNode<T> getNext() {
        return next;
    }
//----------------------------------------------------------------
//  Sets the node that follows this one.
// ----------------------------------------------------------------
public void setNext (LinearNode<T> node) {
        next = node;
    }
//----------------------------------------------------------------
//  Returns the element stored in this node.
// ----------------------------------------------------------------
public T getElement() {
        return element;
    }
public void setElement (T elem) {
        element = elem;
    }
        }

• 以上代码是我和刘先润一起写的，所以相同。我们的代码和书上的代码也有一些不同。我们最初定义了两个节点。一个头结点一个尾节点。在构造函数将头节点指向为节点。在操作中头结点和尾节点都不存储数据。(但是后来发现到时没什么作用，到时代码比之书上并不简洁)

• Android演示Stack

• 我的思路用RecyclerView来完成此次app.

• 1.首先要使用RecyclerView就要先添加依赖

    compile 'com.android.support:cardview-v7:21.0.3'
    compile 'com.android.support:recyclerview-v7:21.0.3'

• 2.定义一个item

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="130dp"
        android:gravity="center"
        android:layout_margin="4dp"
        android:textColor="#99000000"
        android:textStyle="bold"
        android:textSize="22sp"
        android:background="@color/md_blue_100"
        android:text="0"/>
</LinearLayout>

• 3.Activity布局

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="wb.is.besti.edu.cd.mystack.MainActivity">
<LinearLayout
    android:id="@+id/liner"
    android:layout_width="match_parent"
    android:layout_height="60dp"
    android:layout_marginLeft="16dp"
    android:layout_marginRight="16dp"
    android:layout_marginBottom="16dp">
    <EditText
        android:id="@+id/mtext"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>
    <android.support.v7.widget.RecyclerView
        android:id="@+id/list"
        android:clipToPadding="false"
        android:scrollbarStyle="outsideOverlay"
        android:layout_below="@+id/liner"
        android:layout_height="match_parent"
        android:layout_width="wrap_content"></android.support.v7.widget.RecyclerView>
</RelativeLayout>

• 4.menu的布局

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
<item android:id="@+id/action_push"
    android:title="PUSH"
    android:orderInCategory="100"
    app:showAsAction="always"></item>
    <item
        android:id="@+id/action_pop"
        android:title="POP"
        android:orderInCategory="100"
        app:showAsAction="always"></item>
</menu>

• 5.Activity

public class MainActivity extends AppCompatActivity {
    RecyclerView mRecyclerView;
    SimpleAdapter mAdapter;
    EditText mText;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mText = (EditText)findViewById(R.id.mtext);
        mRecyclerView = (RecyclerView)findViewById(R.id.list);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        mRecyclerView.addItemDecoration(new DividerItemDecoration(this,LinearLayoutManager.VERTICAL));
        mAdapter = new SimpleAdapter(this);
        mRecyclerView.setItemAnimator(new DefaultItemAnimator());
        mRecyclerView.setAdapter(mAdapter);
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.popandpush,menu);
        return true;
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        if (id==R.id.action_push){
            mAdapter.push(mText.getText().toString());
            return true;
        }
        if (id==R.id.action_pop){
            mAdapter.remove(SimpleAdapter.LAST_POSITION);
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

• 6.适配器Adapter

public class SimpleAdapter extends RecyclerView.Adapter<SimpleAdapter.SimpleViewHolder> {
    public static  int LAST_POSITION = -1;
    private final Context mContext;
    private MyStack<String> myStack;
    public void push(String s){
        myStack.push(s);
        LAST_POSITION++;
    }
    public void remove(int positon){
        if (myStack.size()==0){
        }
        if (myStack.size()!=0){
            myStack.pop();
            notifyItemRemoved(positon);
        }
    }
    public static class SimpleViewHolder extends RecyclerView.ViewHolder{
        public final TextView title;
        public SimpleViewHolder(View view){
            super(view);
            title = (TextView)view.findViewById(R.id.title);
        }
    }
    public SimpleAdapter(Context context){
        mContext = context;
            myStack = new MyStack<>();
    }
    @Override
    public SimpleViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        final View view = LayoutInflater.from(mContext).inflate(R.layout.simple_item,parent,false);
        return new SimpleViewHolder(view);
    }
    @Override
    public int getItemCount() {
        return myStack.size();
    }
    @Override
    public void onBindViewHolder(SimpleViewHolder holder, int position) {
        holder.title.setText(myStack.peek());
    }
}

• 7.(非必须)添加分割线

• 效果图
  

• RecyclerView是我在完成假期的工作记录APP时了解到的控件，RecyclerView只管回收与复用View，其他的你可以自己去设置。其高度的解耦，给予你充分的定制自由。进一步的加深使用时添加卫星菜单来实现isEmpty(),peek(),size()等操作及将界面进一步美化。