一个冷僻的知识点try直接返回finally里的设置null其实无效

先看引用类型的代码：

import java.util.HashMap;
import java.util.Map;

public class trycatchefinally {
    public static void main(String[] args) {
        System.out.println(getMap().get("KEY"));
    }

    public static Map getMap() {
        Map map = new HashMap<>();
        map.put("KEY", "INIT");

        try {
            map.put("KEY", "TRY");
            System.out.println("111>>> ");
            return map;
        } catch (Exception e) {
            map.put("KEY", "CATCH");
        } finally {
            System.out.println("222>>> ");
            map.put("KEY", "FINALLY");
            map = null;
            System.out.println("333>>> ");
        }
        System.out.println("444>>> ");
        return map;
    }
}

finally里修改map为null 

下面是字节码：

 0 new #8 
 3 dup
 4 invokespecial #9 >
 7 astore_0
 8 aload_0
 9 ldc #4 
11 ldc #10 
13 invokeinterface #11  count 3
18 pop
19 aload_0
20 ldc #4 
22 ldc #12 
24 invokeinterface #11  count 3
29 pop
30 aload_0
31 astore_1
32 aload_0
33 ldc #4 
35 ldc #13 
37 invokeinterface #11  count 3
42 pop
43 aconst_null
44 astore_0
45 aload_1
46 areturn
47 astore_1
48 aload_0
49 ldc #4 
51 ldc #15 
53 invokeinterface #11  count 3
58 pop
59 aload_0
60 ldc #4 
62 ldc #13 
64 invokeinterface #11  count 3
69 pop
70 aconst_null
71 astore_0
72 goto 91 (+19)
75 astore_2
76 aload_0
77 ldc #4 
79 ldc #13 
81 invokeinterface #11  count 3
86 pop
87 aconst_null
88 astore_0
89 aload_2
90 athrow
91 aload_0
92 areturn

下面是注释了try里的return比较生成的不同的字节码：

参考：https://stackoverflow.com/questions/4625650/object-reference-set-to-null-in-finally-block

再看看值类型：

总结如下：

try{ return } finally{…} return

finally修改基本类型，则不影响返回值

finally修改非基本类型，影响返回值