什么时候有条件地发生这个分配？

Question

我正在将一些 Java 代码移植到 Xojo，它没有与 Java 相同的语言结构。

我在端口中有一个错误，我想我已经将它缩小到 Java 代码的这一点：

int maxIndex = 0;
int n = vertices.length; // vertices is an array
double max = dot(vertices[0]), candidateMax; // I'm assuming `candidateMax` is being initialised to 0 here.

if (max < (candidateMax = vector.dot(vertices[1]))) {
  // Search to the right
  do {
    max = candidateMax;
      maxIndex++;
  } while ((maxIndex + 1) < n && max < (candidateMax = vector.dot(vertices[maxIndex + 1])));

} else if ( max < (candidateMax = vector.dot(vertices[n - 1])) ) {
  maxIndex = n;
  // Search to the left
  do {
    max = candidateMax;
     maxIndex--;
  } while (maxIndex > 0 && max <= (candidateMax = vector.dot(vertices[maxIndex - 1])));
}
return maxIndex;

我已将其移植到此代码（Xojo - 比上面的代码更冗长）：

Var maxIndex As Integer = 0
Var n As Integer = Vertices.Count
Var max As Double = vector.Dot(Vertices(0))
Var candidateMax As Double

candidateMax = vector.Dot(Vertices(1))
If max < candidateMax Then
  // Search to the right.
  Do
    max = candidateMax
    maxIndex = maxIndex + 1

    // Exit?
    If maxIndex + 1 >= n Then
      Exit
    Else
      candidateMax = vector.Dot(Vertices(maxIndex + 1))
      If max > candidateMax Then Exit
    End If
  Loop
Else
  candidateMax = vector.Dot(Vertices(n - 1))
  If max < candidateMax Then
    maxIndex = n

    // Search to the left.
    Do
      max = candidateMax
      maxIndex = maxIndex - 1

      // Exit?
      If maxIndex <= 0 Then
        Exit
      Else
        candidateMax = vector.Dot(Vertices(maxIndex - 1))
        If max > candidateMax Then Exit
      End If
    Loop
  End If
End If

Return maxIndex

我假设 while 循环条件：

if (max < (candidateMax = vector.dot(this.vertices[1]))) {
  // Search to the right
  do {
    max = candidateMax;
      maxIndex++;
  } while ((maxIndex + 1) < n && max < (candidateMax = vector.dot(vertices[maxIndex + 1])));

翻译为："Do the contents of the loop at least once. After each iteration of the loop, check to see if maxIndex + 1 is less than n. If it's not then exit the loop. If maxIndex + 1 is greater than n then assign the result of the vector.dot method to candidateMax and check to see if max is less than candidateMax. If it is then keep iterating".

这是正确的吗？我认为我误解了评估 while 条件的顺序。

Answer 1

我相信你弄错了循环退出条件。

原文：

while (maxIndex > 0 && max <= (candidateMax = vector.dot(vertices[maxIndex - 1])))

在 Xojo 中的意思大致是：

  ...
  if maxIndex > 0 then candidateMax = vector.Dot(Vertices(maxIndex - 1))
while (maxIndex > 0) and (max <= candidateMax)

一般来说，您可以将Java/C的do ... while (b)翻译成Xojo的do ... loop until not (b)。

这意味着，在您的情况下：

  ...
  if maxIndex > 0 then candidateMax = vector.Dot(Vertices(maxIndex - 1))
loop until not ( (maxIndex > 0) and (max <= candidateMax) )

什么时候有条件地发生这个分配？

When in a conditional does this assignment occur?

java

xojo