16.类型转换[值类型和引用类型的转换]

1. 值类型

private void Form1_Load(object sender, EventArgs e)
        {
            int a = 6;    //System.int32
            long b=5;    //System .int64
           // b = a;     //隐式转换
            a = (int)b;  //显示转换
           // MessageBox.Show(b + "");
            MessageBox.Show(a+"");
        }

2. 引用类型

（1）

 public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

 

        private void Form1_Load(object sender, EventArgs e)
        {
            Fruit f = new Apple();
            Apple a = (Apple)f;
            MessageBox.Show(a.i+"");
        }
    }
    class Fruit
    {

    }
    class Apple:Fruit
    {
        public int i = 1;
    }

(2)

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

 

        private void Form1_Load(object sender, EventArgs e)
        {
            Fruit f = new Apple();
            if (f is Apple)
            {
                Apple a = (Apple)f;
                MessageBox.Show(a.i+"");
            }
        }
    }
    class Fruit
    {

    }
    class Apple:Fruit
    {
        public int i = 1;
    }

(3)

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

 

        private void Form1_Load(object sender, EventArgs e)
        {
            Fruit f = new Apple();
            Apple a = f as Apple ;
            if (a!=null)
            {
                
                MessageBox.Show(a.i+"");
            }
        }
    }
    class Fruit
    {

    }
    class Apple:Fruit
    {
        public int i = 1;
    }

实例1 

（第一行代码功能是所有的控件都显示在TextBox1里）