// exceptions/DynamicFields.java

// (c)2021 MindView LLC: see Copyright.txt

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

// A Class that dynamically adds fields to itself to

// demonstrate exception chaining

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 };

}

@Override 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());

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);

}

fields[fieldNumber][1] = value;

return result;

}

public static void main(String[] args) {

DynamicFields df = new DynamicFields(3);

System.out.println(df);

try {

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

df.setField("number", 47);

df.setField("number2", 48);

System.out.println(df);

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

df.setField("number3", 11);

System.out.println("df: " + df);

System.out.println("df.getField(\"d\") : "

+ df.getField("d"));

Object field =

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

} catch(NoSuchFieldException |

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:96)

Caused by: java.lang.NullPointerException

at

DynamicFields.setField(DynamicFields.java:66)

... 1 more

*/