java 从 lambda 表达式引用的局部变量必须是最终的
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/40493738/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Local variables referenced from a lambda expression must be final
提问by axiorema
I′m trying to create a getValue()function from a pojo that use summatory of details class values in this sense:
我正在尝试getValue()从 pojo创建一个函数，在这个意义上使用细节类值的汇总：
@Transient
public BigDecimal getValue() {
BigDecimal sum = new BigDecimal(0);
details.stream().forEach((detail) -> {
sum = sum.add(detail.getValue());
});
return sum;
}
but I don't know why this the line sum = sum.add(detail.getValue());provoke this error:
但我不知道为什么这条线sum = sum.add(detail.getValue());会引发此错误：
local variables referenced from a lambda expression must be final or effectively final
从 lambda 表达式引用的局部变量必须是最终的或有效的最终变量
Can you say me what's I'am doing wrong. Thanks.
你能告诉我我做错了什么吗？谢谢。
回答by Louis Wasserman
You cannotmodify variables from inside a lambda. That's just not a thing you're allowed to do.
您不能从 lambda 内部修改变量。这不是你被允许做的事情。
What you cando here is write this method as
你可以在这里做的是把这个方法写成
return details.stream()
.map(Detail::getValue)
.reduce(BigDecimal.ZERO, BigDecimal::add);
回答by axiorema
Ok, just do not use the lambda expression in the foreach loop
好的，只是不要在 foreach 循环中使用 lambda 表达式
@Transient
public BigDecimal getValue() {
BigDecimal sum = new BigDecimal(0);
for (Detail detail : details) {
sum = sum.add(detail.getValue());
}
return sum;
}
回答by Rocky
this is my way to avoid final p in the loop and it worked.
这是我在循环中避免最终 p 的方法并且它起作用了。
public void getSolutionInfo(){
ArrayList<Node> graph = Main.graph;
for(int p=1;p<=Pmax;p++) {
final int p2=p;
System.out.printf("number of node with priority p = %d is %d ",p, graph.stream().filter(node->node.getPriority()==p2).count());
}
