fault，error，failure

最新推荐文章于 2023-03-02 16:57:43 发布

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最新推荐文章于 2023-03-02 16:57:43 发布

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原文链接：http://www.cnblogs.com/silver-nitrate/p/8543751.html

本文分析了两个查找算法中的缺陷，并提供了相应的修正方法。第一个算法是寻找数组中最后一个指定元素的位置，第二个算法则是查找数组中最后一个0的位置。通过具体案例展示了如何识别并修正这些缺陷。

(1)

public int findLast (int[] x, int y) { 
    //Effects: If x==null throw NullPointerException
    // else return the index of the last element 
    // in x that equals y. 
    // If no such element exists, return -1 
    for (int i=x.length-1; i > 0; i--) {
        if (x[i] == y) {
            return i; 
        } 
    } return -1;
} 
// test: x=[2, 3, 5]; y = 2
// Expected = 0

Identify the fault：for (int i = x.length -1; i > 0; i--)处应修改为for (int i = x.length -1; i >= 0; i--)

a test case that does not execute the fault：x=null y=2

a test case that executes the fault, but does not result in an error state：无

a test case that results in an error, but not a failure：x=[3, 2, 5] y = 2

(2)

public static int lastZero (int[] x) { 
    //Effects: if x==null throw NullPointerException
    // else return the index of the LAST 0 in x. 
    // Return -1 if 0 does not occur in x 
    for (int i = 0; i < x.length; i++) {
        if (x[i] == 0) {
            return i;
        }
    } 
     return -1;
}
// test: x=[0, 1, 0] 
// Expected = 2