Is there any difference between these two codes?

Question

@Autowired
private StringRedisTemplate stringRedisTemplate;

public void test(String key) {
    // IDEA prompts an error
    Map<String, String> entries1 = stringRedisTemplate.opsForHash().entries(key);
        
    // This is OK.
    HashOperations<String, String, String> opsForHash = stringRedisTemplate.opsForHash();
    Map<String, String> entries = opsForHash.entries(key);  
}

What error was shown? Can you please post the error message? — deHaar, Sep 29 '20 at 11:01
That means `stringRedisTemplate.opsForHash().entries(key)` returns a `Map — deHaar, Sep 29 '20 at 11:03
@deHaar But why `stringRedisTemplate.opsForHash();` retrun a `HashOperations`, but I am initialized opsForHash as a `HashOperations` is OK — Gray, Sep 29 '20 at 11:12
Similar: [comparing and thenComparing gives compile error](https://stackoverflow.com/questions/40500280/comparing-and-thencomparing-gives-compile-error) — Ole V.V., Sep 29 '20 at 11:22

Roberto · Answer 1 · 2020-10-05T16:10:11.957

The problem Is that the method opsForHash() uses 2 generics, This is the signature:

public <HK, HV> HashOperations<K, HK, HV> opsForHash()

If you want to use a single line, you need to set the generics, just like:

Map<String, String> entries1 = stringRedisTemplate.<String, String>opsForHash().entries(key);

In your code, the second approach works because the compiler finds out the generics from the defined variable on the left side of the = operator.

Is there any difference between these two codes?

1 Answers1