package exceptions;

//: exceptions/DynamicFields.java

// A Class that dynamically adds fields to itself.

// Demonstrates exception chaining.

import static net.mindview.util.Print.*;

class DynamicFieldsException extends Exception {}

public class DynamicFields {

  private Object[][] fields;

  public DynamicFields(int initialSize) {

    fields = new Object[initialSize][2];

    for(int i = 0; i < initialSize; i++)

      fields[i] = new Object[] { null, null };

  }

  public String toString() {

    StringBuilder result = new StringBuilder();

    for(Object[] obj : fields) {

      result.append(obj[0]);

      result.append(": ");

      result.append(obj[1]);

      result.append("\n");

    }

    return result.toString();

  }

  private int hasField(String id) {

    for(int i = 0; i < fields.length; i++)

      if(id.equals(fields[i][0]))

        return i;

    return -1;

  }

  private int

  getFieldNumber(String id) throws NoSuchFieldException {

    int fieldNum = hasField(id);

    if(fieldNum == -1)

      throw new NoSuchFieldException();

    return fieldNum;

  }

  private int makeField(String id) {

    for(int i = 0; i < fields.length; i++)

      if(fields[i][0] == null) {

        fields[i][0] = id;

        return i;

      }

    // No empty fields. Add one:

    Object[][] tmp = new Object[fields.length + 1][2];

    for(int i = 0; i < fields.length; i++)

      tmp[i] = fields[i];

    for(int i = fields.length; i < tmp.length; i++)

      tmp[i] = new Object[] { null, null };

    fields = tmp;

    // Recursive call with expanded fields:

    return makeField(id);

  }

  public Object

  getField(String id) throws NoSuchFieldException {

    return fields[getFieldNumber(id)][1];

  }

  public Object setField(String id, Object value)

  throws DynamicFieldsException {

    if(value == null) {

      // Most exceptions don't have a "cause" constructor.

      // In these cases you must use initCause(),

      // available in all Throwable subclasses.

      DynamicFieldsException dfe =

        new DynamicFieldsException();

      dfe.initCause(new NullPointerException());//除了三种基本异常类,其它类型的异常应该使用initCause()方法

      throw dfe;

    }

    int fieldNumber = hasField(id);

    if(fieldNumber == -1)

      fieldNumber = makeField(id);

    Object result = null;

    try {

      result = getField(id); // Get old value

    } catch(NoSuchFieldException e) {

      // Use constructor that takes "cause":

      throw new RuntimeException(e);//原始异常传递给了新的异常

    }

    fields[fieldNumber][1] = value;

    return result;

  }

  public static void main(String[] args) {

    DynamicFields df = new DynamicFields(3);

    print(df);

    try {

      df.setField("d", "A value for d");

      df.setField("number", 47);

      df.setField("number2", 48);

      print(df);

      df.setField("d", "A new value for d");

      df.setField("number3", 11);

      print("df: " + df);

      print("df.getField(\"d\") : " + df.getField("d"));

      Object field = df.setField("d", null); // Exception

    } catch(NoSuchFieldException e) {

      e.printStackTrace(System.out);

    } catch(DynamicFieldsException e) {

      e.printStackTrace(System.out);

    }

  }

} /* Output:

null: null

null: null

null: null

d: A value for d

number: 47

number2: 48

df: d: A new value for d

number: 47

number2: 48

number3: 11

df.getField("d") : A new value for d

DynamicFieldsException

        at DynamicFields.setField(DynamicFields.java:64)

        at DynamicFields.main(DynamicFields.java:94)

Caused by: java.lang.NullPointerException  //这里通过异常链显示了前一个异常

        at DynamicFields.setField(DynamicFields.java:66)

        ... 1 more

*///:~