Command (NanoDB SQL Relational Database 0.1-SNAPSHOT API)

java.lang.Object
- edu.caltech.nanodb.commands.Command

Direct Known Subclasses:

AnalyzeCommand, BeginTransactionCommand, CommitTransactionCommand, CrashCommand, CreateIndexCommand, CreateTableCommand, CreateViewCommand, DropIndexCommand, DropTableCommand, DumpCommand, ExitCommand, ExplainCommand, FlushCommand, OptimizeCommand, QueryCommand, RollbackTransactionCommand, SetPropertyCommand, ShowPropertiesCommand, ShowSystemStatsCommand, ShowTablesCommand, ShowTableStatsCommand, VerifyCommand
```
public abstract class Command
extends java.lang.Object
```
Abstract base-class for all commands that NanoDB supports. Command classes contain both the arguments and configuration details for the command being executed, as well as the code for actually performing the command. Databases tend to have large switch statements controlling how various commands are handled, and this really isn't a very pretty way to do things. So, NanoDB uses a class-hierarchy for command representation and execution.
The command class is subclassed into various command categories that relate to various operations in the database. For example, the QueryCommand class represents all SELECT, INSERT, UPDATE, and DELETE operations.

Nested Class Summary

Nested Classes
Modifier and Type Class Description

static class Command.Type
Commands are either Data-Definition Language (DDL), Data-Manipulation Language (DML), or utility commands.

Field Summary

Fields
Modifier and Type	Field	Description
`private Command.Type`	`cmdType`	The type of this command.
`protected java.io.PrintStream`	`out`	This is the output stream for the current session, so that command output goes to the appropriate client.

Constructor Summary

Constructors
Modifier Constructor Description

protected Command(Command.Type cmdType)
Create a new command instance, of the specified command-type.

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	Description
`abstract void`	`execute(NanoDBServer server)`	Actually performs the command.
`Command.Type`	`getCommandType()`	Returns the general type or category of this command.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - cmdType
```
private Command.Type cmdType
```
    The type of this command.
  - out
```
protected java.io.PrintStream out
```
    This is the output stream for the current session, so that command output goes to the appropriate client.
- Constructor Detail
  - Command
```
protected Command(Command.Type cmdType)
```
    Create a new command instance, of the specified command-type. The constructor is protected, but that is redundant with the fact that the class is abstract anyways, so this class cannot be constructed directly.
    
    Parameters:
    
    cmdType - the general category of command
- Method Detail
  - getCommandType
```
public Command.Type getCommandType()
```
    Returns the general type or category of this command.
  - execute
```
public abstract void execute(NanoDBServer server)
                      throws ExecutionException
```
    Actually performs the command.
    
    Throws:
    
    ExecutionException - if an issue occurs during command execution