Java内部类应该场景

场景一：当某个类除了它的外部类，不再被其他的类使用时

场景二：解决一些非面向对象的语句块：try{}catch{}finally{}

public interface DataManager { 
    public void manageData(); 
} 

public class DataTemplate{ 
    public void execute(DataManager dm) { 
        try {
            dm.manageData(); 
        } catch(Exception e) { 
            LoggerAgent.error("GetHeaderData", "getDivisionData", "SQLException: " + e); 
            e.printStackTrace();
        }finally{ 
            manager.close(stmt); 
            manager.releaseConnection(conn); 
        } 
    } 
} 

 

new DataTemplate().execute(new DataManager() { 
    public void manageData() { 
        String[] divisionData = null; 
        conn = manager.getInstance().getConnection();
        stmt = (OracleCallableStatement)conn.prepareCall("{ Call PM_GET_PRODUCT.HEADER_DIVISION(?, ?) }"); 
        stmt.setLong(1 ,productId.longValue() ); 
        stmt.registerOutParameter(2, oracle.jdbc.OracleTypes.CURSOR);  
        stmt.execute(); 
        ResultSet rs = stmt.getCursor(2);
        int i = 0  
        String strDivision = ""; 
        while( rs.next() ) { 
            strDivision += rs.getString("DIVISION_ID") + ","  
        } 
        int length = strDivision.length();
        if(length != 0 ) { 
            strDivision = strDivision.substring(0,length - 1);    
        } 
        divisionData = StringUtil.split(strDivision, ",");
        map.put("Division", strDivision );
        LoggerAgent.debug("GetHeaderProcess","getDivisionData","getValue+" + strDivision +" " + productId);
} 
}); 

场景之三：一些多算法场合:

Arrays.sort(emps,new Comparator(){
Public int compare(Object o1,Object o2)
{
return ((Employee)o1).getServedYears()-
((Employee)o2).getServedYears(); 
}
});

场景之四：适当使用内部类，使得代码更加灵活和富有扩展性

package polyFactory; 
public interface Shape { 
    public void draw();
    public void erase(); 
} 

package polyFactory; 
import java.util.HashMap; 
import java.util.Map; 
public abstract class ShapeFactory { 
protected abstract Shape create(); 
private static Map factories = new HashMap(); 
public static void addFactory(String id,ShapeFactory f) { 
    factories.put(id,f); 
} 
public static final Shape createShape(String id) { 
    if(!factories.containsKey(id)) {
    try { 
        Class.forName("polyFactory."+id); 
    } catch(ClassNotFoundException e) {   
        throw new RuntimeException("Bad shape creation : "+id); 
    } 
}
return ((ShapeFactory)factories. get(id)).create();
 }
 } 
  

package polyFactory; 
public class Circle implements Shape { 
    public void draw() {  
        System.out.println("the circle is drawing..."); 
    } 
    public void erase() { 
        System.out.println("the circle is erasing..."); 
    } 
    private static class Factory extends ShapeFactory{ 
        protected Shape create() { 
            return new Circle(); 
        } 
    } 
    static {ShapeFactory.addFactory("Circle",new Factory());} 
} 

package polyFactory; 
public class Square implements Shape { 
    public void draw() { 
        System.out.println("the square is drawing..."); 
    } 
    public void erase() { 
        System.out.println("the square is erasing..."); 
    } 
    private static class Factory extends ShapeFactory  { 
        protected Shape create() {
            return new Square(); 
        } 
    } 
    static {ShapeFactory.addFactory("Square",new Factory());} 
}