Summary

Specialized implementations of the TreeMap methods putIfAbsent, computeIfAbsent, computeIfPresent, compute, and merge are introduced.

Problem

Default implementations of the putIfAbsent, computeIfAbsent, computeIfPresent, compute, and merge methods provided by AbstractMap delegate to the get, put, and remove methods, which may require traversing the tree twice. An optimized implementation can traverse the tree only once. This can provide a noticeable speedup, especially if the comparison method is expensive.

Solution

Provide optimized implementations for these methods, similar to HashMap.

Specification

• As TreeMap now overrides the methods putIfAbsent, computeIfAbsent, computeIfPresent, compute, and merge, the implSpec section specified for the corresponding default methods in the Map interface is no longer relevant to TreeMap methods.

• The specification for the TreeMap method computeIfAbsent now additionally covers the concurrent update policy, as follows:

     * <p>This method will, on a best-effort basis, throw a
     * {@link ConcurrentModificationException} if it is detected that the
     * mapping function modifies this map during computation.
     *
     * @throws ConcurrentModificationException if it is detected that the
     * mapping function modified this map

• The specifications for the TreeMap methods computeIfPresent, compute, and merge now additionally cover the concurrent update policy, as follows:

     * <p>This method will, on a best-effort basis, throw a
     * {@link ConcurrentModificationException} if it is detected that the
     * remapping function modifies this map during computation.
     *
     * @throws ConcurrentModificationException if it is detected that the
     * remapping function modified this map

These additions are exactly copied from the specification of the corresponding HashMap methods.