...

S → SS
S → (S)
S → ()
S → key KEY
KEY → operator OPERATOR
OPERATOR → value VALUE
OPERATOR → value
VALUE → value VALUE
VALUE → value
VALUE → and AND
VALUE → or OR
AND → S
OR → S

Psuedocode

Criteria

...

A wrapper around an in-order collection of symbols. A Criteria is generated from the completion of a state machine that comprises a builder.

Code Block

public class Criteria {   // Static Methods public static Builder builder();  { // Variables privatereturn finalnew List<Symbol> symbolsStartState(new Criteria());   } // Constructorprivate final List<Symbol> symbols = Lists.newArrayList(); protected Criteria();   // Methods protected void addSymbol(Symbol symbol);   public static final Builder {   // Static methods protected static Builder newBuilder();   // Variables private final Criteria criteria; private State state;   // Constructor private Builder(Criteria criteria); }   }

...

}

State

The base class and marker for any valid state for the builder. Each state is passed the current Criteria and holds a reference. For any method called from the state, a symbol is added to the Criteria or the Criteria is returned.

abstract class State {
	Criteria criteria;
} 

StartState

The state that marks the beginning of a new Criteria.

class StartState extends State {
	StartState group(Criteria criteria);
	KeyState key(String key);
	Criteria build();
}

KeyState

The state that expects the next symbol/token to be a key specification.

class KeyState extends State {
	OperatorState operator(Operator operator);
}

OperatorState

The state that expects the next symbol/token to be a value specification.

class OperatorState extends State {
	ValueState value(Object value);
}

ValueState

The state that expects the current symbol/token to be the last or the next symbol/token to be value or conjunction specification.

class ValueState extends State {
	ValueState value(Object value);
	StartState and();
	StartState or();
	Criteria build();
}

Symbol

A marker interface to indicate an object that can be included in a Criteria

...

class Key implements Symbol {
	
	public String getKey();
}

...

class Value implements Symbol {
	
	public Object getValue();
}

State

A state 

abstract class State {
 
	Criteria criteria; 
}

interface Symbol { } //marker interface 
 
KeySymbol implements Symbol {
	String key;
}
 
ValueSymbol implements Symbol {
	Object value; 
}
 
OperatorSymbol implements Symbol {
	Operator operator;
}

...

// When the State creates this symbol it must convert the object to a TObject so that it can be passed over the wire via Thrift
	public TObject getValue();
}

Order of Operations

Given validly formed grouped criteria, we must process everything with the correct order of operations. For this, we should use the Shunting-yard algorithm. I've written this algorithm in PHP so we should port it to Java.

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