java - 查询 if 语句

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”而不是人名。- 如果第 1、第 2 和第 3 条不正确并且返回 n/a，我正在尝试编写 IF 语句。

score 1 · Accepted Answer

不要使用=运算符来比较boolean值——这是赋值运算符，所以它总是true. 它已经boolean，只需使用：

} else if (hasFinished) {

此外， it'sfalse或 it's true，因此不需要第三种情况。你可以删除

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

无论如何，这在语法上是不正确的。

score 0 · Accepted Answer

你永远不会被details += "n/a"处决有两个原因：

您分配hasFinished给（正如其他人指出的那样）true：if
```
else if  (hasFinished = true)
```
它应该是
```
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
    }
}

因此，即使您进行了第一次修复，其背后的逻辑也没有任何意义。您应该在第二个中使用另一个评估if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 {
        ...
    }
}

score 0 · Accepted Answer

基本上，你需要检查你是否真的有三个终结者，这构成了你的 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;
}

如果您希望允许少于三个竞争对手，但仍显示第 1/2/3 个，您可以使用三元比较并将 else-if 子句替换为 else。

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;
}

score 0 · Accepted Answer

=用于赋值，==用于比较。在以下语句中使用==代替：=

else if  (hasFinished = true)

这实际上将分配 hasFinished 值 true 并且条件将始终被评估为 true。将其更改为：

else if  (hasFinished == true)

进行比较而不是分配

java - 查询 if 语句

4 回答 4

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