用 Java 流替换嵌套循环

Question

how can I replace the following code with Streams?

 Annotation[][] annotations = context.getMethod().getParameterAnnotations();
        Object[] parameterValues = context.getParameters();
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = 0; i < annotations.length; i++) {
            for (int j = 0; j < annotations[i].length; j++) {
                if (annotations[i][j] instanceof CacheKey && parameterValues[i] != null) {
                    stringBuilder.append(parameterValues[i]);
                    break;
                }
            }
        }

I can easily use flatmap to get data from the first array of array, but I have no idea how to get the position to fetch the right value from parameterValues[i].

Thanks

Answer 1

You could zip annotations with paremeterValues using some known method , but you should also ask yourself "is this gonna be more readable and better that it already is?". Short answer - no.

You compare parameterValues[i] != null in the inner loop when you can actually extract it level higher (Is this even needed? Ain't parameters not null by default?). You could also replace the inner loop with for-each, or even better refactor to simple matchAny() on stream or (the best) use getAnnotation() . Check also if you can get annotations directly from Parameter, so that it would boil down to a simple:

StringBuilder sb = new StringBuilder();
for (var param : context.getParameters()) {
    if (param != null // is it needed ?
        && param.getAnnotation(CacheKey::class) != null)
        sb.append(param);
}