【Java异常】Variable used in lambda expression should be final or effectively final

package com.example.core.mydemo.java8;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Java8FinalTest {
    public static void main(String[] args) {
        //如果直接定义变量，不会报错”Variable used in lambda expression should be final or effectively final“
//        List<Integer> number = Arrays.asList(1,2,3,4,5,6,7,8,9,10);

        //如果分开赋值，就会报错”Variable used in lambda expression should be final or effectively final“
        List<Integer> number = null;
        number = Arrays.asList(1,2,3,4,5,6,7,8,9,10);

        //创建临时中间变量，可以用final也可以不用final
        final List<Integer> numberTmp = number;
        //Variable used in lambda expression should be final or effectively final
        List<Integer> group = Arrays.asList(1,2);
        List<Object> groupResult = group.stream().map(x -> calc(numberTmp)).collect(Collectors.toList());
        groupResult.stream().forEach(System.out :: println);

        //匿名内部类 1.8不会报错
        //1.7会报错：Variable 'jdkVersion' is accessed from within inner class, needs to be declared final，意思是：变量‘dkVersion’在匿名内部类中被访问，必须被声明为final类型的。
        String jdkVersion = "1.7";
        testFinal(new Suppliers(){
            @Override
            public String get() {
                return jdkVersion;
            }
        });
    }

    public static void testFinal(Suppliers supplier){
        System.out.println("supplier=" + supplier.get());
    }


    private static Object calc(List<Integer> number) {
        //变量不允许修改
//        number.add(11);  Exception in thread "main" java.lang.UnsupportedOperationException
        return number.stream().mapToInt(x -> x).sum();
    }

    static class Suppliers{
        public String get(){
            return "hello world";
        }
    }
}