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最新推荐文章于 2024-04-30 08:45:26 发布

最新推荐文章于 2024-04-30 08:45:26 发布 · 297 阅读

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#TDD #Java

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本文介绍了除法功能从基本实现到逐步完善的过程，包括确保除数不为零及结果格式化等关键步骤，并通过重构提高了代码质量。

关于除法功能的TODO列表
1、基本功能
2、除数不能为零
3、格式化，保留小数点后两位

代码演进过程1：基本功能（列表第一项）


/**测试代码：DivisionTest.java*/
public class DivisionTest extends TestCase {
        //测试基本功能
	public void testDivision() {
	      Division division = new Division();
              //0除以1等于0
	      assertEquals(0.00, division.compute(1, 0));
              //1除以1等于1
              assertEquals(1.00, division.compute(1, 1));
              //2除以1等于2
              assertEquals(2.00, division.compute(1, 2));
	}
}
/**Division.java*/
public class Division implements ICalculator { 
        //计算除法
	public double compute(double divisor, double dividend) {
		return dividend / divisor;
        }
}

代码演进过程2：添加功能-除数不能为零（列表第二项）


/**测试代码：DivisionTest.java*/
public class DivisionTest extends TestCase {
        //测试基本功能
	public void testDivision() {
	        Division division = new Division();
        //0除以1等于0
	        assertEquals(0.00, division.compute(1, 0));
        //1除以1等于1
        assertEquals(1.00, division.compute(1, 1));
        //2除以1等于2
        assertEquals(2.00, division.compute(1, 2));
	}
        //测试除数不能为零
	public void testException() {
		try {
			Division division = new Division();
                        //错误：3除以0
			division.compute(0, 3);
			fail("should throw an exception but not");
		} catch (IllegalArgumentException expected) {
			assertTrue(true);
		}
	}
}
/**Division.java*/
public class Division implements ICalculator { 
    //计算除法
	public double compute(double divisor, double dividend) {
         //检查除数是否为零，若为真则抛出异常
		if (divisor == 0)
			throw new IllegalArgumentException("divisor cannot be zero");
		return dividend / divisor;	
}
}

代码演进过程3：添加功能-格式化（列表第三项）


/**测试代码：DivisionTest.java*/
public class DivisionTest extends TestCase {
    //测试基本功能
	public void testDivision() {
		Division division = new Division();
         //0除以1等于0
		assertEquals(0.00, division.compute(1, 0));
        //1除以1等于1
        assertEquals(1.00, division.compute(1, 1));
        //2除以1等于2
        assertEquals(2.00, division.compute(1, 2));
        //测试格式化
assertEquals(1.33, division.compute(3, 4));
	}
    //测试除数不能为零
	public void testException() {
		try {
			Division division = new Division();
             //错误：3除以0
			division.compute(0, 3);
			fail("should throw an exception but not");
		} catch (IllegalArgumentException expected) {
			assertTrue(true);
		}
	}
}
/**Division.java*/
public class Division implements ICalculator {
//计算除法
//此时格式化功能耦合在计算功能中
	public double compute(double divisor, double dividend) {
DecimalFormat df = new DecimalFormat("#.##");
		if (divisor == 0)
			throw new IllegalArgumentException("divisor cannot be zero");
		return Double.parseDouble(df.format(dividend / divisor));	
}
}

代码演进过程4：重构-把格式化代码分离出去
重构依据：降低程序的耦合性


/**Division.java*/
public class Division implements ICalculator {
    //计算除法
	public double compute(double divisor, double dividend) {
		if (divisor == 0)
			throw new IllegalArgumentException("divisor cannot be zero");
		return format(dividend / divisor);	
}
//格式化运算结果：保留两位有效小数点
	private double format(double value) {
		DecimalFormat df = new DecimalFormat("#.##");
		return Double.parseDouble(df.format(value));
	}
}

最终代码清单


/**计算器接口：ICalculator.java*/
public interface ICalculator {
	double compute(double arg1, double arg2);
}
/**重构后的Division.java*/
public class Division implements ICalculator {
    //计算除法
	public double compute(double divisor, double dividend) {
		if (divisor == 0)
			throw new IllegalArgumentException("divisor cannot be zero");
		return format(dividend / divisor);	
}
//格式化运算结果：保留两位有效小数点
	private double format(double value) {
		DecimalFormat df = new DecimalFormat("#.##");
		return Double.parseDouble(df.format(value));
	}
}
/**测试代码：DivisionTest.java*/
public class DivisionTest extends TestCase {
	public void testDivision() {
		Division division = new Division();
		assertEquals(0.00, division.compute(1, 0));
		assertEquals(1.33, division.compute(3, 4));
	}
	public void testExceptions() {
		try {
			Division division = new Division();
			division.compute(0, 3);
			fail("should throw an exception but not");
		} catch (IllegalArgumentException expected) {
			assertTrue(true);
		}
	}
}

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