Java 编程的动态性，第3部分: 应用反射载

public class PlanGen {
    private boolean m_isConcise;          // rarely used, default false
    private int m_initialRevenue = 1000;  // thousands, default is 1M
    private float m_growthRate = 1.5;     // default is 50% growth rate
    private String m_productDescription = // McD look out, here I come
        "eFood - (Really) Fast Food Online";
    ...
    private int revenueForYear(int year) {
        return (int)(m_initialRevenue * Math.pow(m_growthRate, year-1));
    }
    ...

private static final ParameterDef[] PARM_DEFS = { 
    new BoolDef(‘c‘, "m_isConcise"),
    new IntDef(‘f‘, "m_initialRevenue", 10, 10000),
    new FloatDef(‘g‘, "m_growthRate", 1.0, 100.0),
    new StringDef(‘n‘, "m_productDescription")
}

public class PlanGen
{
    private static final ParameterDef[] PARM_DEFS = {
        ...
    };
    
    public static void main(String[] args) {
    
        // if no arguments are supplied, assume help is needed
        if (args.length > 0) {
        
            // process arguments directly to instance
            PlanGen inst = new PlanGen();
            int next = ArgumentProcessor.processArgs
                (args, PARM_DEFS, inst);
            
            // next unused argument is output file name
            if (next >= args.length) {
                System.err.println("Missing required output file name");
                System.exit(1);
            }
            File outf = new File(args[next++]);
            ...
        } else {
            System.out.println("\nUsage: java PlanGen " +
            "[-options] file\nOptions are:\n  c  concise plan\n" +
            "f  first year revenue (K$)\n  g  growth rate\n" +
            "n  product description");
        }
    }
}

public abstract class ParameterDef
{
    protected char m_char;          // argument flag character
    protected String m_name;        // parameter field name
    protected Field m_field;        // actual parameter field
    
    protected ParameterDef(char chr, String name) {
        m_char = chr;
        m_name = name;
    }
    public char getFlag() {
        return m_char;
    }
    protected void bindToClass(Class clas) {
        try {
        
            // handle the field look up and accessibility
            m_field = clas.getDeclaredField(m_name);
            m_field.setAccessible(true);
            
        } catch (NoSuchFieldException ex) {
            throw new IllegalArgumentException("Field ‘" +
                m_name + "‘ not found in " + clas.getName());
        }
    }
    public abstract void handle(ArgumentProcessor proc);
}

public class ArgumentProcessor
{
    private Object m_targetObject;  // parameter value object
    private int m_currentIndex;     // current argument position
    ...
    public ArgumentProcessor(ParameterDef[] parms, Object target) {
        
        // bind all parameters to target class
        for (int i = 0; i < parms.length; i++) {
            parms[i].bindToClass(target.getClass());
        }
        
        // save target object for later use
        m_targetObject = target;
    }
    
    public void setValue(Object value, Field field) {
        try {
        
            // set parameter field value using reflection
            field.set(m_targetObject, value);
            
        } catch (IllegalAccessException ex) {
            throw new IllegalArgumentException("Field " + field.getName() +
                " is not accessible in object of class " + 
                m_targetObject.getClass().getName());
        }
		}
    
    public void reportArgumentError(char flag, String text) {
      throw new ArgumentErrorException(text + " for argument ‘" + 
        flag + "‘ in argument " + m_currentIndex);
    }
    
    public static int processArgs(String[] args,
        ParameterDef[] parms, Object target) {
        ArgumentProcessor inst = new ArgumentProcessor(parms, target);
        ...
    }
}

public class IntDef extends ParameterDef
{
    private int m_min;              // minimum allowed value
    private int m_max;              // maximum allowed value
    
    public IntDef(char chr, String name, int min, int max) {
        super(chr, name);
        m_min = min;
        m_max = max;
    }
    protected void bindToClass(Class clas) {
        super.bindToClass(clas);
        Class type = m_field.getType();
        if (type != Integer.class && type != Integer.TYPE) {
            throw new IllegalArgumentException("Field ‘" + m_name +
                "‘in " + clas.getName() + " is not of type int");
        }
    }
    public void handle(ArgumentProcessor proc) {
        
        // set up for validating
        boolean minus = false;
        boolean digits = false;
        int value = 0;
        
        // convert number supplied in argument list to ‘value‘
        ...
        
        // make sure we have a valid value
        value = minus ? -value : value;
        if (!digits) {
            proc.reportArgumentError(m_char, "Missing value");
        } else if (value < m_min || value > m_max) {
            proc.reportArgumentError(m_char, "Value out of range");
        } else {
            proc.setValue(new Integer(value), m_field);
        }
    }
}