这个java代码如何执行代码？

Question

I have a project in my programming class and I'm failing a test case. I look into the test driver and find this:

 private static boolean testSquareArch()
  {
  boolean pass = true;
  int test = 1;
  int cnt;
  Square sq;
  Class cl;

  System.out.println("Square architecture tests...");

  sq = new Square(true, true, true, true, 0, 0);

  cl = sq.getClass();
  cnt = cl.getFields().length;
  pass &= test(cnt == 5, test++);  //FAILING THIS TEST

What does this do and how does it check my code?

Also while I'm here, what does this do?

  // Count and test number of of PACKAGE fields
  cnt = cl.getDeclaredFields().length
      - countModifiers(cl.getDeclaredFields(), Modifier.PRIVATE)
      - countModifiers(cl.getDeclaredFields(), Modifier.PROTECTED)
      - countModifiers(cl.getDeclaredFields(), Modifier.PUBLIC);
  pass &= test(cnt == 5, test++);  // Test 8 

I'm failing these test cases and just want to know why. Thanks

Answer 1

If you are asking about the &= assignment operator, it keeps the variable true only if the right side argument is also true (if it was already false, it will stay false). It works just like += and a &= b is the same as a = a & b , the operator & being the boolean conjuction (AND).

 pass &= test(cnt == 5, test++); 

is shorthand for

 if( ! test( cnt == 5, test ) )
     pass = false;
 test++;

I assume that it is part of unit testing code and asserts that cnt == 5, also counting the number of tests and the total result (pass or fail).

Using Junit, you do not have to manually take care of the number of tests, or the end result, and you could write

assertEquals("count is correct", 5, cnt);

This will also produce useful output to help figure out exactly what failed (such as the value of an incorrect count).

Answer 2

它似乎是在检查您在班级中声明了多少个字段，以及其中有多少是私人可见性。

Answer 3

If you're wondering about &= , here's a quote from JLS 15.22.2. Boolean Logical Operators &, ^, and | .

For &, the result value is true if both operand values are true; otherwise, the result is false.

The operators & and | for booleans are the lesser known cousins of && ( 15.23 ) and || ( 15.24 ). The latter two are "conditional" operators; they short-circuit and only evaluate the right hand side if it's actually needed.

The && operator is like & (§15.22.2), but evaluates its right-hand operand only if the value of its left-hand operand is true .

&= is the compound assignment version of & . See JLS 15.26.2. Compound Assignment Operators .

A compound assignment expression of the form E1 op= E2 is equivalent to E1 = (T)((E1) op (E2)), where T is the type of E1, except that E1 is evaluated only once.

In other words, these are equivalent (assumed boolean b ):

b &= bool_expr;
b = b & bool_expr;
if (!bool_expr) b = false;

---

This may also be your issue ( java.lang.Class#getDeclaredFields ):

Returns an array of Field objects reflecting all the fields declared by the class or interface represented by this Class object. This includes public, protected, default (package) access, and private fields, but excludes inherited fields .

Your count may not be correct if you want to also count the inherited fields.

Answer 4

In Java the namespaces for variables and methods don't conflict. So it looks like the driver has both a variable and a method called "test".

Without the test() method and your own source code, it is hard to say what is wrong, but it looks like you have the wrong number of fields in your Square class. (There should be five.)

Answer 5

是的，似乎需要更多的字段来完成声明，这应该修复命名空间。