I. Introduction
After analyzing the finished List two major classes, we have to analyze the Set interface classes under, HashSet and LinkedHashSet, in fact, after the completion of the analysis HashMap and LinkedHashMap, let's analyze HashSet and LinkedHashSet, it will become very simple, begin the analysis below .
Second, the data structure
2.1 HashSet data structure
Old rules, the first data structure, because the bottom is HashSet HashMap or LinkedHashMap based implementation, the data structure is HashSet HashMap or LinkedHashMap data structure, as has already been analyzed, so no cumbersome. Direct look here, the HashMap JDK1.8 source code analysis of (a) && JDK1.8 source code analysis of a LinkedHashMap (II) .
2.2 LinkedHashSet data structure
LinkedHashSet based LinkedHashMap implemented, the data structures directly see here. JDK1.8 source code analysis of LinkedHashMap (two) .
Third, source code analysis
3.1 HashSet
1. class inheritance
public class HashSet<E>
extends AbstractSet<E>
implements Set<E>, Cloneable, java.io.Serializable
2. The class of property
public class HashSet<E>
extends AbstractSet<E>
implements Set<E>, Cloneable, java.io.Serializable
{
// version serial number
static final long serialVersionUID = -5024744406713321676L;
// key Map
private transient HashMap<E,Object> map;
// used as a value corresponding to all the keys, the key values are equal to corresponding
private static final Object PRESENT = new Object();
}
Description: HashSet due contains only key, does not contain a value, since the underlying specific implementation, the use or a LinkedHashMap HashMap (constructors can be specified to determine which structure to use), we know that the key is stored HashMap, so in order to adaptation storage HashMap, HashSet PRESENT adds a class field (all category), all the keys have the same value (PRESENT).
3. Other analysis
add, contains, remove or operating functions are based HashMap do LinkedHashMap, source code analysis have been previously given, not cumbersome.
3.2 LinkedHashSet
1. class inheritance
public class LinkedHashSet<E>
extends HashSet<E>
implements Set<E>, Cloneable, java.io.Serializable
Description LinkedHashSet inherited from HashSet, also implements a number of interfaces, not cumbersome.
2. Other notes
LinkedHashSet will call the parent class constructor HashSet, let the underlying implementation is LinkedHashMap, so to achieve a good functional LinkedHashSet need.
IV Summary
HashSet, LinkedHashSet and HashMap, LinkedHashMap, respectively. After analyzing the HashMap, LinkedHashMap source, HashSet, LinkedHashSet also a very easy to understand. Thank you Friends of the Park Watch ~