Java Generics and Collections by By

Author:By
Language: eng
Format: epub
ISBN: 0-596-52775-6
Publisher: O'Reilly
Published: 2011-10-04T19:40:10.973088+00:00

An advanced Strategy pattern with recursive bounds

abstract class TaxPayer<P extends TaxPayer<P>> { public long income; // in cents private TaxStrategy<P> strategy; public TaxPayer(long income, TaxStrategy<P> strategy) { this.income = income; this.strategy = strategy; } protected abstract P getThis(); public long getIncome() { return income; } public long computeTax() { return strategy.computeTax(getThis()); } } class Person extends TaxPayer<Person> { public Person(long income, TaxStrategy<Person> strategy) { super(income, strategy); } protected Person getThis() { return this; } } class Trust extends TaxPayer<Trust> { private boolean nonProfit; public Trust(long income, boolean nonProfit, TaxStrategy<Trust> strategy){ super(income, strategy); this.nonProfit = nonProfit; } protected Trust getThis() { return this; } public boolean isNonProfit() { return nonProfit; } } interface TaxStrategy<P extends TaxPayer<P>> { public long computeTax(P p); } class DefaultTaxStrategy<P extends TaxPayer<P>> implements TaxStrategy<P> { private static final double RATE = 0.40; public long computeTax(P payer) { return Math.round(payer.getIncome() * RATE); } } class DodgingTaxStrategy<P extends TaxPayer<P>> implements TaxStrategy<P> { public long computeTax(P payer) { return 0; } } class TrustTaxStrategy extends DefaultTaxStrategy<Trust> { public long computeTax(Trust trust) { return trust.isNonprofit() ? 0 : super.computeTax(trust); } }

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