什么样的 Java 语法是“== null？false:true;”
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What kind of Java syntax is "== null? false:true;"
提问by tzippy
I am looking through code and wondering what this means:
我正在查看代码并想知道这意味着什么：
Boolean foo = request.getParameter("foo") == null? false:true;
It's gotta be something that converts the returning String from getParameter() into a Boolean.
它必须是将 getParameter() 返回的 String 转换为布尔值的东西。
But I've never seen this kind of Java with a questionmark and colon (except in a foreach loop). Any hel appreciated!
但我从未见过这种带有问号和冒号的 Java（除了在 foreach 循环中）。任何人都表示赞赏！
采纳答案by paxdiablo
It's the ternary operator. The snippet:
这是三元运算符。片段：
Boolean foo = request.getParameter("foo") == null? false:true;
is equivalent to:
相当于：
Boolean foo;
if (request.getParameter("foo") == null)
foo = false;
else
foo = true;
or (optimised):
或（优化）：
Boolean foo = request.getParameter("foo") != null;
The basic form of the operator is along the lines of:
运算符的基本形式如下：
(condition) ? (value if condition true) : (value if condition false)
回答by NullUserException
That's the ternary operator:
那是三元运算符：
(condition) ? if-true : if-false
The whole thing could've been written as:
整个事情可以写成：
Boolean foo = request.getParameter("foo") != null;
Which IMO is cleaner code.
哪个 IMO 是更干净的代码。
回答by Zaki
It is shorthand for
它是简写
Boolean foo;
if(request.getParameter("foo")==null)
{
foo = false;
}
else { foo = true; }
回答by Thorbj?rn Ravn Andersen
The ?:is an ifyou can have insidean expression.
该?:是if你可以有内部的表达式。
The Java Tutorial describes it here: http://download-llnw.oracle.com/javase/tutorial/java/nutsandbolts/op2.html
Java 教程在这里对其进行了描述：http: //download-llnw.oracle.com/javase/tutorial/java/nutsandbolts/op2.html
(go to ConditionalDemo2)
（转到 ConditionalDemo2）
回答by kocka
The whole thing could be just
整件事可能只是
Boolean foo = (request.getParameter("foo") != null);
