没有括号的Java if语句会产生意外行为

Question

为什么这样做有效：

if(name.equals("email_stub")) {
    if(emailStub == "")
        emailStub = results.getString("text");
} else if(name.equals("fax")) {
    if(fax == "")
        fax = results.getString("text");
} 

但如果没有第一层括号，它将无法工作，反而无法在逻辑上分隔if语句。i、 e.它永远不会超出第一个if语句，也不会按预期工作

if(name.equals("email_stub"))
    if(emailStub == "")
        emailStub = results.getString("text");
else if(name.equals("fax"))
    if(fax == "")
        fax = results.getString("text");

当我遇到这个问题时，我觉得很奇怪

Answer 1

因为：

if(name.equals("email_stub"))
    if(emailStub == "")
        emailStub = results.getString("text");
else if(name.equals("fax"))
    if(fax == "")
        fax = results.getString("text");

实际上是这样的：

if(name.equals("email_stub"))
    if(emailStub == "")
        emailStub = results.getString("text");
    else if(name.equals("fax"))
        if(fax == "")
            fax = results.getString("text");

如果没有花括号，else将引用它前面的第一个if

---

正如@Hovercraft所评论的：

Avoid if(emailStub == "") and instead do if (emailStub.isEmpty()) or if ("".equals(emailStub)) since you should never compare Strings with == or !=. Also consider use of trim() here, such as if (emailStub.trim().isEmpty()).

见How do I compare strings in Java?