Question

public String toString() {

String details = number + ", " + RACE_DESCRIPTIONS[typeIndex] + "[" + date + "]" + ":";
if (!hasFinished) {
  details += "Race not finished";
} else if  (hasFinished = true) {
  details += "\n     1st: " + competitors[0].getName();
  details += "\n     2nd: " + competitors[1].getName();
  details += "\n     3rd: " + competitors[2].getName();
} else if {
  details += "n/a"; 
}
return details;

如果尚未设置位置，则应返回字符串文字“n / a”而不是该人的姓名。 - 我试图写一个IF语句，如果第1，第2和第3不是真的，而是返回n / a。

Answer 1

请勿使用=运算符来比较boolean值 - 即赋值运算符，因此始终为true。它已经boolean，只需使用：

} else if (hasFinished) {

此外，无论是false还是true，都不需要第三种情况。你可以删除

else if {
  details += "n/a"; 
}

无论如何，

在语法上是不正确的。

Answer 2

=用于分配，==用于比较。在以下语句中使用==代替=：

else if  (hasFinished = true)

这实际上会将hasFinished值赋值为true，并且条件也将始终计算为true。将其更改为：

else if  (hasFinished == true)

进行比较而不是分配

Answer 3

由于两个原因，您永远不会执行details += "n/a"：

您在hasFinished中为true分配了if（正如其他人所说）：
```
else if  (hasFinished = true)
```
应该是
```
else if  (hasFinished)
```

最重要的是，您的代码具有以下形式：

if (false) {
    ...
} else {
    if (true) {
    } else {
        //this is false, it was supposed to be hitted before
    }
}

所以即使你做了第一次修复，背后的逻辑也没有任何意义。您应该在第二个if中使用另一个评估来处理最后一个else语句。例如：

if (!hasFinished) {
    ...
} else {
    //the hasFinished usage here has no sense, being commented
    //just left it to show this is supported
    //if (hasFinished && someValue <= someOtherValue) {
    if (someValue <= someOtherValue) {
        ...
    } else {
        ...
    }
}

Answer 4

基本上，你需要检查一下你是否真的有三个终结者，这就构成了你的else-if子句。

public String toString()
{
    String details = number + ", " + RACE_DESCRIPTIONS[typeIndex] + "[" + date + "]" + ":";
    if(!hasFinished) // The race has not yet finished.
    {
        details += "Race not finished";
    }
    else if(competitors.length >= 3) // Implies that hasFinished evaluated to true
    {
        details += "\n     1st: " + competitors[0].getName();
        details += "\n     2nd: " + competitors[1].getName();
        details += "\n     3rd: " + competitors[2].getName();
    }
    else // The race has finished, but there are less than three competitors
    {
        details += "n/a";
    }
    return details;
}

如果你想允许少于三个竞争者，但仍然显示第一/第二/第三，你可以使用三元比较并用else替换你的else-if子句。

public String toString()
{
    String details = number + ", " + RACE_DESCRIPTIONS[typeIndex] + "[" + date + "]" + ":";
    if(!hasFinished)
    {
        details += "Race not finished";
    }
    else // Implies that hasFinished evaluated to true
    {
        details += "\n     1st: " + (competitors.length >= 1 ? competitors[0].getName() : "n/a");
        details += "\n     2nd: " + (competitors.length >= 2 ? competitors[1].getName() : "n/a");
        details += "\n     3rd: " + (competitors.length >= 3 ? competitors[2].getName() : "n/a");
    }
    return details;
}

询问if语句

4 个答案: