1. Timestamp problem: date class and calendar class in jdk 1.7 have problems in processing timestamps. For example, when dealing with time zone conversion, there will be errors due to daylight saving time adjustment.

2. Thread safety: The concurrenthashmap class in jdk 1.7 has thread safety problems, such as deadlock when multiple threads access concurrently.

3. Memory leak: There is a memory leak in the arraylist class in jdk 1.7, such as frequently adding and deleting elements.