Local variable sumWrapper defined in an enclosing scope must be final or effectively final如何解决

这个错误是因为在使用Lambda表达式时，变量需要是final或者effectively final的。

解决方法：

1. 将sumWrapper声明为final：

final Integer sumWrapper = new Integer(sum);

2. 不使用Lambda表达式，而是使用匿名内部类：

for (int i = 0; i < 1000; i++) {
    new Thread(new Runnable() {
        @Override
        public void run() {
            synchronized (sumWrapper) {
                sumWrapper = sumWrapper + 1;
            }
        }
    }).start();
}

这两种方法都可以解决这个错误。需要注意的是，第二种方法在语法上比较繁琐，但是在某些情况下可能更加灵活，可以根据实际情况选择使用哪种方法。

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。