各位看官們,大家好,上一回中咱們說的是Java中類集之Set
的例子,這一回咱們繼續說該例子。閒話休提,言歸正轉。讓我們一起Talk Android吧!
看官們,我們在前面章回中介紹了Set接口和它的實現類HashSet
。本章回中將介紹Set接口的另外一個實現類TreeSet
。TreeSet
表示有序的集合,而HashSet
表示無序的集合,這是它們之間的不同點。這個順序不是指按照輸入數據時的順序,它是按照Comparable
接口中compareTo()
方法的結果來排序的。因此使用TreeSet
存放自定義的數據類型時,需要實現該接口。存放內置數據類型時就不需要了。
TreeSet
可以向HashSet
一樣添加或者刪除數據,不過因爲TreeSet
集合是有序集合,所以添加或者刪除數據會對集合排序,以保證整個集合的有序性。除此之外,它還有一些自己特有的方法:
first()和last()
用來返回集合第一個和最後一個元素headSet(obj)和tailSet(obj)
用來返回在obj元素前面和後面所有元素組成的集合subSet(from,to)
返回 從from到to這個“區間”內元素組成的集合
這些操作涉及的大於或者小於某個數據元素,大於或者小於的比較是基於equals()和hashCode()
方法,而且大於操作包含元素本身,可以看作是大於等於某個數據,小於操作則不包含元素本身(可以通過程序運行結果看出來)。
準確來講TreeSet
是SortedSet
接口的實現類,而SortedSet
接口又是Set
接口的子接口,因此可以把TreeSet
類看作是Set
接口的實現類。不過在代碼中最好把TreeSet
類對象轉換爲SortedSet
接口對象,而不是Set
接口對象,不然好多方法無法使用。下面是具體的代碼,請參考:
import java.util.Arrays;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
public class setEx {
public static void main(String args[]){
// init set
SortedSet<Integer> set = new TreeSet<>();
for (int i = 0; i < 10; ++i) {
// set.add(new Integer(i+1));
set.add((i + 1));
}
// show size of set ,and content of set
System.out.println("size of set: " + set.size());
for (Integer i : set)
System.out.print(i + " ");
System.out.println("\nset: " + set);
// delete the content of set,this is based on content of set
if(set.remove(9)) {
System.out.println("after removing the content 9. set: " + set);
} else {
System.out.println("removing the content 9 failed.");
}
// delete the same content of set,it is failed to remove
if(set.remove(9)) {
System.out.println("after removing the content 9. set: " + set);
} else {
System.out.println("removing the content 9 failed.");
}
// add the same content of set,it is failed to add
if(set.add(9)) {
System.out.println("after adding the content 9. set: " + set);
} else {
System.out.println("adding the content 9 failed.");
}
// add the content of set,this is based on content of set
if(set.add(9)) {
System.out.println("after adding the content 9. set: " + set);
} else {
System.out.println("adding the content 9 failed.");
}
// change set to array
Integer[] array = set.toArray(new Integer[] {});
System.out.println("change set to array: " + Arrays.toString(array));
//------------ this is for TreeSet ---------------
System.out.println("TreeSet operation: first: "+set.first() );
System.out.println("TreeSet operation: last: "+set.last() );
System.out.println("TreeSet operation: headSet 6: "+set.headSet(6) );
System.out.println("TreeSet operation: TailSet 6: "+set.tailSet(6) );
System.out.println("TreeSet operation: subSet[3,9]: "+set.subSet(3,9));
//------------ this is for TreeSet ---------------
// add the content of set,this is based on content of set
set.clear();
System.out.println("after clearing the set: " + set);
}
}
下面是程序的運行結果,請參考:
size of set: 10
1 2 3 4 5 6 7 8 9 10
set: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
after removing the content 9. set: [1, 2, 3, 4, 5, 6, 7, 8, 10]
removing the content 9 failed.
after adding the content 9. set: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
adding the content 9 failed.
change set to array: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
TreeSet operation: first: 1
TreeSet operation: last: 10
TreeSet operation: headSet 6: [1, 2, 3, 4, 5]
TreeSet operation: TailSet 6: [6, 7, 8, 9, 10]
TreeSet operation: subSet[3,9]: [3, 4, 5, 6, 7, 8]
after clearing the set: []
各位看官,關於Java中類集之Set的例子咱們就介紹到這裏,欲知後面還有什麼例子,且聽下回分解!