BTreeLeaf delete and insert methods

[yunshengtw]

Hi,

I'm wondering why delete and insert methods are restricted to be called only once, immediately after construction? As the other part of the description as well as the method naming seem to me that chances are these methods might be called multiple times.

vanillacore/src/main/java/org/vanilladb/core/storage/index/btree/BTreeLeaf.java

Lines 268 to 278 in 793e3a3

	/**
	* Inserts a new B-tree leaf record having the specified data record ID and
	* the previously-specified search key. This method can only be called once,
	* immediately after construction.
	*
	* @param dataRecordId
	* the data record ID of the new record
	* @return the directory entry of the newly-split page or null of there is
	* no split
	*/
	public DirEntry insert(RecordId dataRecordId) {

vanillacore/src/main/java/org/vanilladb/core/storage/index/btree/BTreeLeaf.java

Lines 357 to 365 in 793e3a3

	/**
	* Deletes the B-tree leaf record having the specified data record ID and
	* the previously-specified search key. This method can only be called once,
	* immediately after construction.
	*
	* @param dataRecordId
	* the data record ID whose record is to be deleted
	*/
	public void delete(RecordId dataRecordId) {