声纳严重违规 - 以前取消引用的Nullcheck值 [英] Sonar critical violation - Nullcheck of value previously dereferenced

问题描述

对于我在我的一个测试类中的下面一段代码，Sonar抛出了一个严重的违规行为 - 正确性 - 以前取消引用的价值的Nullcheck

For the below piece of code I have in one of my test classes, Sonar throws me a critical violation - Correctness - Nullcheck of value previously dereferenced

 if (testLst != null && !testLst.isEmpty()) {
        for (Test test : testLst) {
            if (test.getName().equalsIgnoreCase("TEST")) {
            // do blah
            }

有人可以关于我在这里做错了什么呢？

Can someone throw some light on this on what am I doing wrong here?

编辑：这里的答案之一建议这是因为我之前可以访问变量，所以空检查是多余的。但事实并非如此。这是我的空检查之前的代码行。

One of the answers here suggested this is because I could have accessed the variable before, and so the null check is redundant. That's not true though. Here is the line of code before my null check.

 testLst = myTest.getValues(); //I am basically populating the array by doing a get, but I am not accessing the list itself by doing a get on it directly - like testLst.get()
 if (testLst != null && !testLst.isEmpty()) {
            for (Test test : testLst) {
                if (test.getName().equalsIgnoreCase("TEST")) {
                // do blah
                }

推荐答案

当您检查时会显示此消息如果变量的值为null（在本例中为 testLst ），则之前已经访问过该变量。不需要空检查，因为如果值为null，则抛出 NullPointerException 。

This message is shown when you're checking if a variable's value is null (in this case testLst) whereas you already accessed the variable before. The null check is not needed since if the value was null, a NullPointerException would have been thrown.

示例：

testLst.remove(something);
if (testLst != null && !testLst.isEmpty()) {
    for (Test test : testLst) {
       if (test.getName().equalsIgnoreCase("TEST")) {
        // do blah
        }

支票 testLst！= null 是多余的，因为当程序到达 if 语句时， testLst 不能为null，否则前面的语句 testLst.remove（某事物）会抛出 NullPointerException 。在这种情况下，您应该在访问 testLst 之前，在 为空的地方放置空检查：

The check testLst != null is redundant since at the time the program reaches the if statement, testLst cannot be null, otherwise the previous statement testLst.remove(something) would have thrown a NullPointerException. In this case, you should place the null check before accessing testLst, in a place where it can be null:

if(testLst != null) {
   testLst.remove(something);
   if (!testLst.isEmpty()) {
       for (Test test : testLst) {
          if (test.getName().equalsIgnoreCase("TEST")) {
           // do blah
          }

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