请使用Java语言实现如下税率计算： 1~5000 税率 0 5001~8000 3% 8001~17000 10% 17001~30000 20% 30001~40000 25% 40001~60000 30% 60001~85000 35% 85001~ 45% 要求 ⅰ. 逻辑正确，代码优雅 ⅱ. 可扩展性，考虑区间的变化，比如说起征点从5000变成10000等等，或者说85000以上的征税50%。 ⅲ. 推荐使用合适的设计模式 这里举个例子，比如说税前10000元，5000部分是不扣税，后面5000，3000扣税3%，2000扣税10%。 public class TaxCalculator { public double calculateTax(int amount) { // TODO } } 不用if语句

可以使用责任链模式来实现税率计算，如下所示：

首先定义一个责任链节点抽象类TaxHandler，用来处理税率计算的各个阶段：

public abstract class TaxHandler {
    protected TaxHandler successor;

    public void setSuccessor(TaxHandler successor) {
        this.successor = successor;
    }

    public abstract double handle(double income);
}

然后定义具体的责任链节点类，分别对应税率区间：

public class TaxHandler0 extends TaxHandler {
    @Override
    public double handle(double income) {
        if (income <= 5000) {
            return 0.0;
        } else {
            return successor.handle(income);
        }
    }
}

public class TaxHandler3 extends TaxHandler {
    @Override
    public double handle(double income) {
        if (income <= 8000) {
            return 0.03 * (income - 5000);
        } else {
            return successor.handle(income);
        }
    }
}

public class TaxHandler10 extends TaxHandler {
    @Override
    public double handle(double income) {
        if (income <= 17000) {
            return 0.1 * (income - 8000) + new TaxHandler3().handle(8000);
        } else {
            return successor.handle(income);
        }
    }
}

public class TaxHandler20 extends TaxHandler {
    @Override
    public double handle(double income) {
        if (income <= 30000) {
            return 0.2 * (income - 17000) + new TaxHandler10().handle(17000);
        } else {
            return successor.handle(income);
        }
    }
}

public class TaxHandler25 extends TaxHandler {
    @Override
    public double handle(double income) {
        if (income <= 40000) {
            return 0.25 * (income - 30000) + new TaxHandler20().handle(30000);
        } else {
            return successor.handle(income);
        }
    }
}

public class TaxHandler30 extends TaxHandler {
    @Override
    public double handle(double income) {
        if (income <= 60000) {
            return 0.3 * (income - 40000) + new TaxHandler25().handle(40000);
        } else {
            return successor.handle(income);
        }
    }
}

public class TaxHandler35 extends TaxHandler {
    @Override
    public double handle(double income) {
        if (income <= 85000) {
            return 0.35 * (income - 60000) + new TaxHandler30().handle(60000);
        } else {
            return successor.handle(income);
        }
    }
}

public class TaxHandler45 extends TaxHandler {
    @Override
    public double handle(double income) {
        return 0.45 * (income - 85000) + new TaxHandler35().handle(85000);
    }
}

其中，每个节点都有一个successor属性，表示下一个处理节点，如果当前节点无法处理，则会将请求传递给下一个节点来处理。

最后，在TaxCalculator中组装责任链，并调用责任链节点来计算税率：

public class TaxCalculator {
    private static final int THRESHOLD = 5000; // 起征点

    private TaxHandler taxHandler;

    public TaxCalculator() {
        TaxHandler0 handler0 = new TaxHandler0();
        TaxHandler3 handler3 = new TaxHandler3();
        TaxHandler10 handler10 = new TaxHandler10();
        TaxHandler20 handler20 = new TaxHandler20();
        TaxHandler25 handler25 = new TaxHandler25();
        TaxHandler30 handler30 = new TaxHandler30();
        TaxHandler35 handler35 = new TaxHandler35();
        TaxHandler45 handler45 = new TaxHandler45();

        handler0.setSuccessor(handler3);
        handler3.setSuccessor(handler10);
        handler10.setSuccessor(handler20);
        handler20.setSuccessor(handler25);
        handler25.setSuccessor(handler30);
        handler30.setSuccessor(handler35);
        handler35.setSuccessor(handler45);

        taxHandler = handler0;
    }

    public double calculateTax(int amount) {
        double income = amount - THRESHOLD; // 扣除起征点后的收入
        if (income <= 0) {
            return 0.0;
        } else {
            return taxHandler.handle(income);
        }
    }
}

这样，我们就可以根据税前收入来计算税率，而且可以方便地扩展税率区间，并且可以调整起征点。