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8.0

Type safeing my class.

Asked by PaulCaswell in Java Programming Language

Tags: Java, EnumSet, Generics

Hi All,

I've put together a class that helps me manipulate database tables quite succinctly and it works quite well. See the <unsafe> code below ...

Note that I have cut down the code for posting purposes to the point where it won't actually work but I hope it demonstrates my problem.

I am now trying to make it type safe and I'm having difficulties typeing the EnumSets. See SafeChangeTable and SafeTable.

In particular I am trying to remove the use of EnumSet. My first attempt was the obvious:

public String updateQuery ( EnumSet<Column> key, Column[] columns ) {

but this gives me the error:

type parameter Column is not within its bound

A bit of research found one method:

public String updateQuery (EnumSet<? extends Enum<Column>> key, Column[] columns ) {

which removes the error but then when I try:

public String updateQuery (EnumSet<? extends Enum<Column>> key) {
// If columns not supplied, assume all columns.
return ( updateQuery(key, columns) );
}

I get the error:

cannot find symbol; symbol : method updateQuery(java.util.EnumSet<? extends java.lang.Enum<Column>>,Column[]), location: class SafeTable<Column>

Is EnumSet<? extends Enum<Column>> the right way of doing this? If so, how do I avoid the second error?

Thanks in advance.

Paul

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             // .... <Unsafe version using Enum> ...
 
public class ChangeTable extends Table {
  static final Map<Enum,Field.Type> columnTypes = new HashMap<Enum,Field.Type>();
  
  enum Column {
      Change(Field.Type.String),
      Date(Field.Type.Long);
 
      // Keep track of the column types.
      Column(Field.Type type) {
        columnTypes.put(this, type);
      }
  };
  
  public ChangeTable () {
    super("ChangeTable", Column.values(), columnTypes);
  }
}
 
public class Table {
  final String tableName;
  final Enum[] columns;
  final Map<Enum,Field.Type> types;
  Map<Enum,Object> values = new HashMap<Enum,Object>();
  
  protected Table (String tableName, Enum [] columns, Map<Enum,Field.Type> types) {
    this.tableName = tableName;
    this.columns = columns;
    this.types = types;
  }
 
  // Returns a query that will update all records matching the key.
  private String updateQuery ( EnumSet key, Enum[] columns ) {
    String query = "UPDATE "+tableName+" SET ";
    // SET - All update columns not in key.
    for ( int i = 0; i < columns.length; i++ ) {
      Enum col = columns[i];
      // Not key column.
      if ( !key.contains(col) ) {
        // Add field to query.
        query += col.name() + " = " + values.get(col).toString();
      }
    }
    // WHERE All columns in key.
    query += " WHERE " + keyValues(key);
    return query;
  }
 
  public String updateQuery (EnumSet key) {
    // If columns not supplied, assume all columns.
    return ( updateQuery(key, columns) );
  }
 
  public String updateQuery (EnumSet key, EnumSet updateColumns) {
    // Allow an EnumSet of Columns to update.
    return updateQuery(key, (Enum[]) updateColumns.toArray() );
  }
 
  private String keyValues ( EnumSet key ) {
    String keyValues = "";
    for ( Iterator i = key.iterator(); i.hasNext(); ) {
      // Pull out the column.
      Enum col = (Enum)i.next();
      String val = values.get( col ).toString();
      keyValues += col.name() + " = " + val;
    }
    return keyValues;
  }
 
}
 
public class Field {
  
  enum Type {
    String,
    Long;
  }
  
  public Field () {
  }
}
 
// .... <Attempt at safe version, not using Enum but still using EnumSet> ... 
 
public class SafeChangeTable extends SafeTable<SafeChangeTable.Column> {
  static final Map<Column,Field.Type> columnTypes = new HashMap<Column,Field.Type>();
 
  enum Column {
      Change(Field.Type.String),
      Date(Field.Type.Long);
 
      // Keep track of the column types.
      Column(Field.Type type) {
        columnTypes.put(this, type);
      }
  };
 
  public SafeChangeTable () {
    super("ChangeTable", Column.values(), columnTypes);
  }
}
 
public class SafeTable<Column extends Enum> {
  final String tableName;
  final Column[] columns;
  final Map<Column,Field.Type> types;
  Map<Column,Object> values = new HashMap<Column,Object>();
 
  protected SafeTable (String tableName, Column [] columns, Map<Column,Field.Type> types) {
    this.tableName = tableName;
    this.columns = columns;
    this.types = types;
  }
 
  public String updateQuery ( EnumSet key, Column[] columns ) {
    String query = "UPDATE "+tableName+" SET ";
    // SET - All update columns not in key.
    for ( int i = 0; i < columns.length; i++ ) {
      Column col = columns[i];
      // Not key column.
      if ( !key.contains(col) ) {
        // Add field to query.
        query += col.name() + " = " + values.get(col);
      }
    }
    // WHERE All columns in key.
    query += " WHERE " + keyValues(key);
    return query;
  }
 
  public String updateQuery (EnumSet key) {
    // If columns not supplied, assume all columns.
    return ( updateQuery(key, columns) );
  }
 
  public String updateQuery (EnumSet key, EnumSet updateColumns) {
    // Allow an EnumSet of Columns to update.
    return updateQuery(key, (Column[]) updateColumns.toArray() );
  }
 
  private String keyValues ( EnumSet key ) {
    String keyValues = "";
    for ( Iterator i = key.iterator(); i.hasNext(); ) {
      // Pull out the column.
      Enum col = (Enum)i.next();
      String val = values.get( col ).toString();
      keyValues += col.name() + " = " + val;
    }
    return keyValues;
  }
 
}

           
         

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Type safeing my class.

Asked by PaulCaswell in Java Programming Language

Tags: Java, EnumSet, Generics

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