You need to model a conditional statement with functors.

Use an IfClosure, supplying a Predicate and two Closure objects. If the Predicate evaluates to true, the first Closure is executed; if the Predicate evaluates to false, the second Closure is executed. The following closure deals with a financial decision; a Predicate, isWinning, evaluates a Stock object. If the purchase price is less than the current price, the stock is a winner, causing the buy Closure to be executed. If the purchase price is higher than the current price, the stock is a loser and it is sold by passing it to the sell Closure:

Closure sell = new Closure( ) {
    public void execute(Object input) {
        Stock stock = (Stock) input;
        stock.sell( stock.getShares( ) );
        System.out.println( "\tSold all shares" );
    }
}
Closure buy = new Closure( ) {
    public void execute(Object input) {
        Stock stock = (Stock) input;
        int buyShares = stock.getShares( ) * 0.10;
        stock.buy( buyShares );
        System.out.println( "\tBought " + buyShares );
    }
}
Predicate isWinning = new Predicate( ) {
    public boolean evaluate(Object object) {
        Stock stock = (Stock) object;
        if( stock.getPurchasePrice( ) < stock.getCurrentPrice( ) ) {
            System.out.println( stock.getSymbol( ) + " is a winner";
            return true;
        } else {
            System.out.println( stock.getSymbol( ) + " is a loser";
            return false;
        }
    }
}
Closure stockAction = new IfClosure( isWinning, buy, sell );
Stock yahoo = new Stock("YHOO");
yahoo.setPurchasePrice( 10.0 );
yahoo.setCurrentPrice( 20.0 );
yahoo.setShares( 100 ); 
Stock tibco = new Stock("TIB");
tibco.setPurchasePrice( 50.0 );
tibco.setCurrentPrice( 30.0 );
tibco.setShares( 50 );
// Execute the IfClosure, take action on stocks based on performance
stockAction.execute( yahoo );
stockAction.execute( tibco );

The example evaluates two stocks, a winner and a loser. The following output is generated:

YHOO is a winner
    Bought 10 shares
TIB is a loser
    Sold All Shares

Because an IfClosure is an implementation of a Closure, you can nest IfClosures within other IfClosures. The following code uses the Closure objects and the Predicate defined in the Solution, adding a third Closure, isUnchanged, to create a nested IfClosure--sellOrHold:

Predicate isUnchanged = new Predicate( ) {
    public boolean evaluate(Object object) {
        Stock stock = (Stock) object;
        if( stock.getPurchasePrice( ) == stock.getCurrentPrice( ) ) {
            System.out.println( stock.getSymbol( ) + " is unchanged";
            return true;
        }
        return false;
    }
}
Closure sellOrHold = new IfClosure( isUnchanged, new NOPClosure( ), sell );
Closure stockAction = new IfClosure( isWinning, buy, sellOrHold );
Stock tibco = new Stock("TIB");
tibco.setPurchasePrice( 50.0 );
tibco.setCurrentPrice( 30.0 );
tibco.setShares( 50 );
Stock lucent = new Stock("LU");
tibco.setPurchasePrice( 30.0 );
tibco.setCurrentPrice( 30.0 );
tibco.setShares( 150 );
stockAction.execute( tibco );
stockAction.execute( lucent );

When stockAction is executed, and a Stock does not satisfy the isWinning Predicate, it is passed to the sellOrHold Closure, which is another IfClosure. The sellOrHold Closure then evaluates the Stock to see if it is a loser or unchanged. If the stock price is unchanged, it is passed to a NOPClosure, which performs no operation on the Stock object. If the stock price is less than the purchase price, the Stock is passed to the sell Closure.