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📜  Java TreeSet类

📅  最后修改于: 2020-10-12 09:58:39             🧑  作者: Mango

Java TreeSet类

Java TreeSet类实现了Set接口，该接口使用树进行存储。它继承了AbstractSet类并实现了NavigableSet接口。 TreeSet类的对象以升序存储。

关于Java TreeSet类的要点是：

  • Java TreeSet类仅包含唯一元素，例如HashSet。
  • Java TreeSet类的访问和检索时间非常安静。
  • Java TreeSet类不允许使用null元素。
  • Java TreeSet类不同步。
  • Java TreeSet类维护升序。

TreeSet类的层次结构

如上图所示，Java TreeSet类实现了NavigableSet接口。 NavigableSet接口按层次结构顺序扩展了SortedSet，Set，Collection和Iterable接口。

TreeSet类声明

我们来看一下java.util.TreeSet类的声明。

public class TreeSet extends AbstractSet implements NavigableSet, Cloneable, Serializable

Java TreeSet类的构造方法

Constructor Description
TreeSet() It is used to construct an empty tree set that will be sorted in ascending order according to the natural order of the tree set.
TreeSet(Collection c) It is used to build a new tree set that contains the elements of the collection c.
TreeSet(Comparator comparator) It is used to construct an empty tree set that will be sorted according to given comparator.
TreeSet(SortedSet s) It is used to build a TreeSet that contains the elements of the given SortedSet.

Java TreeSet类的方法

Method Description
boolean add(E e) It is used to add the specified element to this set if it is not already present.
boolean addAll(Collection c) It is used to add all of the elements in the specified collection to this set.
E ceiling(E e) It returns the equal or closest greatest element of the specified element from the set, or null there is no such element.
Comparator comparator() It returns comparator that arranged elements in order.
Iterator descendingIterator() It is used iterate the elements in descending order.
NavigableSet descendingSet() It returns the elements in reverse order.
E floor(E e) It returns the equal or closest least element of the specified element from the set, or null there is no such element.
SortedSet headSet(E toElement) It returns the group of elements that are less than the specified element.
NavigableSet headSet(E toElement, boolean inclusive) It returns the group of elements that are less than or equal to(if, inclusive is true) the specified element.
E higher(E e) It returns the closest greatest element of the specified element from the set, or null there is no such element.
Iterator iterator() It is used to iterate the elements in ascending order.
E lower(E e) It returns the closest least element of the specified element from the set, or null there is no such element.
E pollFirst() It is used to retrieve and remove the lowest(first) element.
E pollLast() It is used to retrieve and remove the highest(last) element.
Spliterator spliterator() It is used to create a late-binding and fail-fast spliterator over the elements.
NavigableSet subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) It returns a set of elements that lie between the given range.
SortedSet subSet(E fromElement, E toElement)) It returns a set of elements that lie between the given range which includes fromElement and excludes toElement.
SortedSet tailSet(E fromElement) It returns a set of elements that are greater than or equal to the specified element.
NavigableSet tailSet(E fromElement, boolean inclusive) It returns a set of elements that are greater than or equal to (if, inclusive is true) the specified element.
boolean contains(Object o) It returns true if this set contains the specified element.
boolean isEmpty() It returns true if this set contains no elements.
boolean remove(Object o) It is used to remove the specified element from this set if it is present.
void clear() It is used to remove all of the elements from this set.
Object clone() It returns a shallow copy of this TreeSet instance.
E first() It returns the first (lowest) element currently in this sorted set.
E last() It returns the last (highest) element currently in this sorted set.
int size() It returns the number of elements in this set.

Java TreeSet示例

Java TreeSet示例1：

让我们看一个简单的Java TreeSet示例。

import java.util.*;
class TreeSet1{
 public static void main(String args[]){
  //Creating and adding elements
  TreeSet al=new TreeSet();
  al.add("Ravi");
  al.add("Vijay");
  al.add("Ravi");
  al.add("Ajay");
  //Traversing elements
  Iterator itr=al.iterator();
  while(itr.hasNext()){
   System.out.println(itr.next());
  }
 }
}

输出：

Ajay
Ravi
Vijay

Java TreeSet示例2：

让我们看一个以降序遍历元素的示例。

import java.util.*;
class TreeSet2{
 public static void main(String args[]){
 TreeSet set=new TreeSet();
 set.add("Ravi");
 set.add("Vijay");
 set.add("Ajay");
 System.out.println("Traversing element through Iterator in descending order");
 Iterator i=set.descendingIterator();
 while(i.hasNext())
 {
 System.out.println(i.next());
 }
 
 }
}

输出：

Traversing element through Iterator in descending order
Vijay
Ravi
Ajay
Traversing element through NavigableSet in descending order
Vijay
Ravi
Ajay

Java TreeSet示例3：

让我们看一个示例来检索和删除最高和最低价值。

import java.util.*;
class TreeSet3{
 public static void main(String args[]){
 TreeSet set=new TreeSet();
 set.add(24);
 set.add(66);
 set.add(12);
 set.add(15);
 System.out.println("Highest Value: "+set.pollFirst());
 System.out.println("Lowest Value: "+set.pollLast());
 }
}

输出：

Highest Value: 12
Lowest Value: 66

Java TreeSet示例4：

在此示例中，我们执行各种NavigableSet操作。

import java.util.*;
class TreeSet4{
 public static void main(String args[]){
  TreeSet set=new TreeSet();
 set.add("A");
 set.add("B");
 set.add("C");
 set.add("D");
 set.add("E");
 System.out.println("Initial Set: "+set);
 
 System.out.println("Reverse Set: "+set.descendingSet());
         
 System.out.println("Head Set: "+set.headSet("C", true));

 System.out.println("SubSet: "+set.subSet("A", false, "E", true));
 
 System.out.println("TailSet: "+set.tailSet("C", false));
 }
}

输出：

Initial Set: [A, B, C, D, E]
Reverse Set: [E, D, C, B, A]
Head Set: [A, B, C]
SubSet: [B, C, D, E]
TailSet: [D, E]

Java TreeSet示例4：

在此示例中，我们执行各种SortedSetSet操作。

import java.util.*;
class TreeSet4{
 public static void main(String args[]){
  TreeSet set=new TreeSet();
 set.add("A");
 set.add("B");
 set.add("C");
 set.add("D");
 set.add("E");
 
 System.out.println("Intial Set: "+set);
 
 System.out.println("Head Set: "+set.headSet("C"));

 System.out.println("SubSet: "+set.subSet("A", "E"));
 
 System.out.println("TailSet: "+set.tailSet("C"));
 }
}

输出：

Intial Set: [A, B, C, D, E]
Head Set: [A, B]
SubSet: [A, B, C, D]
TailSet: [C, D, E]

Java TreeSet示例：书籍

让我们看一个TreeSet示例，其中我们要添加书籍以进行设置并打印所有书籍。 TreeSet中的元素必须为Comparable类型。默认情况下，String和Wrapper类是Comparable的。要在TreeSet中添加用户定义的对象，您需要实现Comparable接口。

import java.util.*;
class Book implements Comparable{
int id;
String name,author,publisher;
int quantity;
public Book(int id, String name, String author, String publisher, int quantity) {
this.id = id;
this.name = name;
this.author = author;
this.publisher = publisher;
this.quantity = quantity;
}
public int compareTo(Book b) {
if(id>b.id){
return 1;
}else if(id set=new TreeSet();
//Creating Books
Book b1=new Book(121,"Let us C","Yashwant Kanetkar","BPB",8);
Book b2=new Book(233,"Operating System","Galvin","Wiley",6);
Book b3=new Book(101,"Data Communications & Networking","Forouzan","Mc Graw Hill",4);
//Adding Books to TreeSet
set.add(b1);
set.add(b2);
set.add(b3);
//Traversing TreeSet
for(Book b:set){
System.out.println(b.id+" "+b.name+" "+b.author+" "+b.publisher+" "+b.quantity);
}
}
}

输出：

101 Data Communications & Networking Forouzan Mc Graw Hill 4
121 Let us C Yashwant Kanetkar BPB 8
233 Operating System Galvin Wiley 6