从 Java 中的 Map 中删除 Class object 密钥

Question

I have a Map with a key/value pair made up of a string and class object Block . The remove(Object key, Object value) method fails to actually remove the object specified.

private static Map<String, ArrayList<Block>> stockInfo = new LinkedHashMap<>();

My IDE tips me off that my entry in the Object value data field " may not contain values of type 'Block' " What fundamental concept am I missing about Java and passing values in methods? I have only been coding in Java for a short period.

stockInfo.remove(symbolCode, (stockInfo.get(symbolCode)).get(0));

Answer 1

I have a Map with a key/value pair made up of a string and class object Block.

No, you don't.

You declared a mapping of String to a collection of objects of type Block . Specifically an ArrayList collection.

So the compiler refuses your attempt to remove a string-to-block entry because there are no such entries. You have only string-to-list-of-blocks entries in your Map .

Map<String, ArrayList<Block>> stockInfo = new LinkedHashMap<>();

A mapping of string to block would look like this:

Map< String, Block > 

Answer 2

stockInfo.remove(symbolCode, (stockInfo.get(symbolCode)).get(0));

What do you want to remove? if you have three block objects, eg:

Block block1 = new Block(); 
Block block2 = new Block();
Block block3 = new Block();
List list1 = new ArrayList();
list1.add(block1);
list1.add(block2);
List list2 = new ArrayList();
list2.add(block2);
list2.add(block3);

what is in your map? like this:

"12" ---> {block1, block2}; "23" ---> {block2, block3};

you want to delete the object block1 with the key "12"?