一.重构实践

实践题目：重构获取指定数值内的所有质数的方法

单元测试案例：

package training.generatPrimes.test;

import static org.junit.Assert.*;

import org.junit.Test;

import training.generatPrimes.PrimeGenerator;

public class PrimeGeneratorTest {

	@Test
	public void testPrimes() {
		int[] nullArray = new PrimeGenerator().generatePrimes(0);
		assertEquals(0,nullArray.length);

		int[] minArray = new PrimeGenerator().generatePrimes(2);
		assertEquals(1,minArray.length);
		assertEquals(2,minArray[0]);

		int[] threeArray = new PrimeGenerator().generatePrimes(3);
		assertEquals(2,threeArray.length);
		assertEquals(2,threeArray[0]);
		assertEquals(3,threeArray[1]);

		int[] centArray = new PrimeGenerator().generatePrimes(100);
		assertEquals(25,centArray.length);
		assertEquals(97,centArray[24]);
	}

	@Test
	public void testExhaustive() {
		for (int i = 2; i < 500; i++) {
			verifyPrimeList(new PrimeGenerator().generatePrimes(i));
		}
	}

	private void verifyPrimeList(int[] list) {
		for (int i = 0; i < list.length; i++) {
			verifyPrime(list[i]);
		}
	}

	private void verifyPrime(int n) {
		for (int factor = 2; factor < n; factor++) {
			assertTrue(n % factor != 0);
		}
	}
}

重构前：

package training.generatPrimes;

/**
 * Refactorings:
 * 
 * Extract Fields.
 * Extract Methods: initArrayOfIntegers,crossOutMultiples,putUncrossedIntegerIntoResult
 * Inline s with f.length
 * Rename f to isCrossed
 * Ensure for loop starts from 2
 * Extract Methods: crossOutMultipleOf,numberOfUncrossedIntegers,notCrossed
 * Rename methods to: uncrossIntegersUpTo
 */
public class PrimeGenerator {
	/**
	 * 
	 * @param maxValue
	 *            is the generation limit
	 * @return
	 */
	public int[] generatePrimes(int maxValue) {
		if (maxValue >= 2) { // the only valid case
			// declarations
			int s = maxValue + 1; // size of array
			boolean[] f = new boolean[s];

			// initialize array to true
			for (int i = 0; i < s; i++) {
				f[i] = true;
			}

			// get rid of known non-primes
			f[0] = f[1] = false;

			// sieve
			for (int i = 2; i < Math.sqrt(s) + 1; i++) {
				for (int j = 2 * i; j < s; j += i) {
					f[j] = false; // multiple is not prime
				}
			}

			// how many primes are there?
			int count = 0;
			for (int i = 0; i < s; i++) {
				if (f[i])
					count++; // bump count
			}

			int[] primes = new int[count];

			// move the primes into the result
			for (int i = 0,j = 0; i < s; i++) {
				if (f[i])
					primes[j++] = i;
			}

			return primes;
		} else { // maxValue < 2
			return new int[0]; // return null array if bad input.
		}
	}
}

package training.generatPrimes;

/**
 * Refactorings:
 * 
 * Extract Fields.
 * Extract Methods: initArrayOfIntegers,notCrossed
 * Rename methods to: uncrossIntegersUpTo
 */
public class PrimeGenerator {
	
	private boolean[] composite;
	
	/**
	 * 
	 * @param maxValue
	 *            is the generation limit
	 * @return
	 */
	public int[] generatePrimes(int maxValue) {
		initArrayOfIntegers(maxValue);
		markAllMultiplesToComposite();
		return getPrimes();
	}

	/**
	 * @param maxValue
	 */
	private void initArrayOfIntegers(int maxValue) {
		composite = new boolean[maxValue + 1];
	}

	/**
	 * @return
	 */
	private int[] getPrimes() {
		int[] primes = new int[numberOfPrimes()];

		for (int i = 2,j = 0; i < composite.length; i++) {
			if (!composite[i])
				primes[j++] = i;
		}
		return primes;
	}

	/**
	 * @return
	 */
	private int numberOfPrimes() {
		int count = 0;
		for (int i = 2; i < composite.length; i++) {
			if (!composite[i])
				count++; // bump count
		}
		return count;
	}

	/**
	 * @param s
	 * @param composite
	 */
	private void markAllMultiplesToComposite() {
		for (int i = 2; i < Math.sqrt(composite.length) + 1; i++) {
			markMultiplesToComposite(i);
		}
	}

	/**
	 * @param composize
	 * @param i
	 */
	private void markMultiplesToComposite(int i) {
		for (int j = 2 * i; j < composite.length; j += i) {
			composite[j] = true; // multiple is not prime
		}
	}
}

二.重构理论知识

1.什么样的代码需要重构
1).Don't Repeat Yourself
2).注释《会说话的代码》－王洪亮，注释代码的意图（写Why)
3).Naming命名
4).Long Method长方法
　a.Performance Anxiety(性能)
b.Scattered Code Avoidance(避免锁碎的代码)
c.Rampant Growth(时间紧急)
d.Bind Conformity(团队环境就是长方法)
e.Pure lgnorance(我不知道什么是好代码，我也不知道怎么写好代码)
5).Large Class(巨类)
6).Dead Code(僵尸代码)
　Kill the dead:Knowledge（知识）、Expenece（经验）、Tools（工具）、Coverage（覆盖）、complexity（复杂度）、Timing（时机）
7).Switch statuement(开关语句)
8).Inappropriate Intimacy(过度亲密),应该调对方的接口
9).复杂条件
10).Magic Number(魔法数字)
11).SingleTon单例(不利测试)

2.重构常用方法
1).重命名2).抽取方法3).内联变量4).反转逻辑5).移动6).删除3.重构注意事项：1).不改变原功能2).频繁运行测试案例3).尽量使用工具4).基于代码坏味道5).步子要小6).重构时只做重构，如果原来逻辑有问题，重构后再处理