Labs
In this lab we will use the debugger to examine changes in the HashMap class as we add data to it.
Package HashMapInternals/com.example.hashmap.labs
- Open
USStatesAppand look through the code, making sure you understand it.
Find the line that constructs a new USState object, and set a breakpoint at that line. Now debug the program using Eclipse's Debug perspective.
In the Variables view: * UN-check the Show Logical Structures button.
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In the View Menu, under Java, check the Show Null Array Entries option.
In the Variables view find and expand states and select its table property. This will be null until the first entry is added. Now use Step Over to advance to the next line. Step Over again and watch as the states HashMap initializes its table array and its internal state.
Expand table to see the new entry and which bucket it was placed in. Open up the node to see the key and value properties.
Use Step Out to continue execution and loop back to the breakpoint. Watch the table array and the modCount field as the next entry is added. Continue repeating Step Out until the modCount reaches 8. Expand table element [1], and follow the next links to see how the HashMap linked the entries in bucket 1.
Continue with Step Over until modCount reaches 12. When you Step Out to add the next entry, watch how a larger table is allocated, and the entries are rehashed to new buckets. What bucket is AR in now? How about CT?
Continue stepping until modCount reaches 24. When you step to add the next entry, how big is the new table? Can you find AR?