Cedar老师的java中的反射学习笔记(二)--动态加载

静态加载:

     编译时刻加载类

     (1)new创建对象是静态加载类,在编译时加载类

动态加载:

    运行时刻加载类

     (2)Class c=Class.forName() 动态加载类

                           c.newInstance();

代码:

(1)创建一个office类:

class Office 
{
	public static void main(String[] args) 
	{
		Word w=new Word();
		w.start();

        Excel e=new Excel();
		e.start();
	}
}

  

   编译后报错:

C:\Users\SheroHuo\Desktop\test>javac office.java
office.java:5: error: cannot find symbol
        Word w=new Word();
        ^
  symbol:   class Word
  location: class Office
office.java:5: error: cannot find symbol
        Word w=new Word();
                   ^
  symbol:   class Word
  location: class Office
office.java:8: error: cannot find symbol
        Excel e=new Excel();
        ^
  symbol:   class Excel
  location: class Office
office.java:8: error: cannot find symbol
        Excel e=new Excel();
                    ^
  symbol:   class Excel
  location: class Office
4 errors

 

       new创建对象是静态加载类,在编译时加载类,因为没有word和excel类。

 

(2)创建word类:

class Word 
{
	public void start(){
	System.out.println("word....start");
	}
}

   编译word 在编译office

编译结果:

C:\Users\SheroHuo\Desktop\test>javac Word.java

C:\Users\SheroHuo\Desktop\test>javac Office.java
Office.java:8: error: cannot find symbol
        Excel e=new Excel();
        ^
  symbol:   class Excel
  location: class Office
Office.java:8: error: cannot find symbol
        Excel e=new Excel();
                    ^
  symbol:   class Excel
  location: class Office
2 errors

  有时候word或excel可能不会用到,希望采用动态加载:

创建一个新的OfficeNew类,通过类类型创建对象。

class OfficeNew 
{
	public static void main(String[] args) 
	{    
		try{
		Class c=Class.forName(args[0]);
		OfficeAll oa=(OfficeAll)c.newInstance();  //通过类类型创建对象
		oa.start();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
}

  创建一个标准-接口:OfficeAll,使word excel实现这个接口:

interface OfficeAll
{
	public void start();
}

  

class Word implements OfficeAll
{
	public void start(){
	System.out.println("word....start");
	}
}

  分别编译word,OfficeNew,再运行word方法:

C:\Users\SheroHuo\Desktop\test>javac Word.java
C:\Users\SheroHuo\Desktop\test>javac OfficeNew.java C:\Users\SheroHuo\Desktop\test>java OfficeNew Word word....start

  

 

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