Local variable i defined in an enclosing scope must be final or effectively final是什么意思

这个错误是Java编译器在使用lambda表达式时提示的错误。它的意思是，当你在lambda表达式中使用一个局部变量时，这个变量必须是final或者是事实上的final。这是因为lambda表达式可以访问外部作用域中的变量，但是这些变量必须是不可变的，否则会导致线程安全问题。如果你在lambda表达式中对这个变量进行了赋值，那么这个变量就不再是final或者是事实上的final了，因此编译器会报错。

以下是几种解决办法：
1. 将变量声明为final或者是事实上的final，即在初始化后不再对其进行赋值。
2. 将变量声明为成员变量，而不是局部变量。
3. 将变量声明为AtomicInteger或者AtomicLong等线程安全的类型，这样就可以在lambda表达式中对其进行修改。

相关问题

Local variable row defined in an enclosing scope must be final or effectively final

The error message "Local variable row defined in an enclosing scope must be final or effectively final" is related to the concept of closures in Java. In Java, when you define a local variable inside an enclosing scope (such as a method or a loop), and you want to use that variable inside an anonymous inner class or lambda expression, the variable needs to be either final or effectively final.

A variable is effectively final if its value is not changed after initialization. If you try to modify the value of a non-final or non-effectively final variable inside an inner class or lambda expression, you will encounter this error.

To resolve this issue, you can either make the variable "row" final or effectively final by not modifying its value after initialization, or you can use a different approach, such as using a different variable or passing the value of "row" to the inner class or lambda expression explicitly.

Here's an example of making the variable final:

final int row = 10;
Runnable runnable = new Runnable() {
    @Override
    public void run() {
        System.out.println("Row: " + row);
    }
};

And here's an example of effectively final variable:

int row = 10;
Runnable runnable = () -> {
    System.out.println("Row: " + row);
};

Remember, if you modify the value of the "row" variable after its initialization, you will encounter the mentioned error.

Local variable answer defined in an enclosing scope must be final or effectively final

这是一个编译时错误，意思是在一个封闭的作用域内定义的局部变量必须是 final 或 effectively final（即在定义后不能再被修改），否则会导致编译错误。这个规则的目的是为了确保代码的可读性和可维护性，因为 final 或 effectively final 的变量在代码执行过程中不会发生变化，更容易让人理解和维护。如果你需要在封闭的作用域内修改变量，则应该使用其他方式，例如将变量定义为属性或使用 lambda 表达式等。