Whether to use the code comparison of the merge method
Do not use merge
Map<Byte, Integer> counts = new HashMap<>();
for (byte b : bytes) {
Integer count = counts.get(b);
if (count == null) {
// Map仍然没有该字符数据
counts.put(b, 1);
} else {
counts.put(b, count + 1);
}
}
Use merge
Map<Byte, Integer> counts = new HashMap<>();
for (byte b : bytes) {
// Map仍然没有该字符数据
counts.merge(b, 1, Integer::sum);
}
merge source code
defaultV merge(K key, V value,
BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
Objects.requireNonNull(remappingFunction);
Objects.requireNonNull(value);
V oldValue = get(key);
//1.给的key值的value为空，赋值newValue. 如果给的key值的value不为空，使用传过来的函数处理 oldValue和 newValue
V newValue = (oldValue == null) ? value :
remappingFunction.apply(oldValue, value);
//若果处理后的newValue为空，移除当前值
if(newValue == null) {
remove(key);
} else {
//若果处理后的newValue为空， put操作
put(key, newValue);
}
return newValue;
}
This method receives three parameters, a key value, a value, and a remappingFunction. If the given key does not exist, it becomes put(key, value). However, if the key already has some values, we can choose the merge method for remappingFunction, and then assign the merged newValue to the original key.