hashmap implementation in java

Java Collection framework 08 -- HashMap and source code analysis1. Introduction to HashMap First, let's take a look at the inheritance relationship of HashMap. java.lang.Object ? java.util.AbstractMap ? java.util.HashMap public class HashMap

Move * with a power of two offset in the new table. * * @return The table */FINAL node[] Resize () {node[] oldtab = table; int Oldcap = (Oldtab = null)? 0:oldtab.length; int oldthr = threshold; int Newcap, newthr = 0; /* If the length of the old table is not empty/if (Oldcap > 0) {if (Oldcap >= maximum_capacity) {threshold = I Nteger. Max_value; return oldtab; /* * Set the length of the new table to twice times the length of the old table

for the second principle, interested persons can refer to Bruce Eckel's "Thinking in Java", where there is an introduction to the principle of hashmap internal implementation, here will not repeat.With these two principles in hand, you will be able to write your own program with good HashMap. I don't know. No, there a

of a hashmap. If multiple hashcode () values fall into the same bucket, the values are stored in a list. In the worst case, all the keys are mapped to the same bucket, so the hashmap degenerate into a list-the lookup time from O (1) to O (n). Let's first test the performance of HashMap in Java 7 and

: If a Thread-safe implementation is not needed, it's recommended to use HASHMAP in place of Hashtable. If a thread-safe highly-concurrent implementation is desired and then it's recommended to use Java.util.concurrent.Concurren Thashmap in place of Hashtable. Simply put, if you don't need thread safety, then use

Float.isnan (loadfactor))Throw NewIllegalArgumentException ("Illegal load factor:" +loadfactor); //Find a power of 2 >= initialcapacity//you need to pay attention here . intCapacity = 1; while(Capacity initialcapacity) Capacity; //setting the load factor This. Loadfactor =Loadfactor; //set the next critical value for expansionThreshold = (int) Math.min (capacity * Loadfactor, maximum_capacity + 1); //initializing a hash tableTable =NewEntry[capacity]; Usealthashing= sun.misc.VM.isBooted

. It is mainly reflected in the java. lang. ThreadLocal class, and is not supported by Java keywords, such as static and transient.1. AbstractMap abstract class and SortedMap InterfaceAbstractMap abstract class: (HashMap inherits AbstractMap) overwrites the equals () and hashCode () methods to ensure that the two equal mappings return the same hash code. If the t

, but will increase the search time and reduce the fill factor, it improves data query performance, but increases the memory space occupied by Hash tables. When a new hashMap is created, the size to be created can be input appropriately, which should be the n power of 2.Underlying Implementation of HashSet The underlying layer of a HashSet is implemented through HashMap