Java 中 TreeSet headSet()方法示例
原文:https://www . geeksforgeeks . org/treeset-headset-method-in-Java-with-examples/
TreeSet 是 Java 中 SortedSet 接口最重要的实现之一，它使用树进行存储。无论是否提供明确的比较器，元素的顺序都由一组使用它们的自然顺序来维护。如果要正确实现设置界面，这必须与 equals 一致。
TreeSet 类的 HEADEMENT()方法已经存在于 java.util 包中，用作树集的限制设置器，以排序的方式返回方法参数中定义的限制内的元素，不包括元素。
语法:
head_set = (TreeSet)tree_set.headSet(Object element)
参数:参数元素属于树集合的类型，并且是头点，该头点是除了元素本身之外树允许返回值的上限。
返回值:该方法以排序的方式返回严格小于参数中提到的元素的那部分值。
现在我们将讨论在 TreeSet 类中实现 headSet()方法时的不同场景:
- 情况 1: 在排序的树集中
- 情况 2-A: 在未排序的树集中
- 情况 2-B: 在未排序但具有字符串类型元素的树集中
例 1:
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to Illustrate headSet() method
// of TreeSet class In a sorted TreeSet
// Importing required classes
import java.io.*;
import java.util.Iterator;
import java.util.TreeSet;
// Main class
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an empty TreeSet by
// declaring object of TreeSet class
TreeSet<Integer> tree_set = new TreeSet<Integer>();
// Adding the elements
// using add() method
tree_set.add(1);
tree_set.add(2);
tree_set.add(3);
tree_set.add(4);
tree_set.add(5);
tree_set.add(10);
tree_set.add(20);
tree_set.add(30);
tree_set.add(40);
tree_set.add(50);
// Creating the headSet tree
TreeSet<Integer> head_set = new TreeSet<Integer>();
// Limiting the values till 5
head_set = (TreeSet<Integer>)tree_set.headSet(30);
// Creating an Iterator
Iterator iterate;
iterate = head_set.iterator();
// Displaying the tree set data
System.out.println(
"The resultant values till head set: ");
// Holds true till there is single element
// remaining in the object
while (iterate.hasNext()) {
// Iterating through the headSet
// using next() method
System.out.println(iterate.next() + " ");
}
}
}
Output:
The resultant values till head set:
1
2
3
4
5
10
20
例 2-A:
Java 语言(一种计算机语言，尤用于创建网站)
// Java Program to illustrate headSet() method
// of TreeSet class In an unsorted TreeSet
// Importing required classes
import java.io.*;
import java.util.Iterator;
import java.util.TreeSet;
// Main class
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an empty TreeSet
TreeSet<Integer> tree_set = new TreeSet<Integer>();
// Adding the elements
// using add() method
tree_set.add(9);
tree_set.add(2);
tree_set.add(100);
tree_set.add(40);
tree_set.add(50);
tree_set.add(10);
tree_set.add(20);
tree_set.add(30);
tree_set.add(15);
tree_set.add(16);
// Creating the headSet tree
TreeSet<Integer> head_set = new TreeSet<Integer>();
// Limiting the values till 5
head_set = (TreeSet<Integer>)tree_set.headSet(30);
// Creating an Iterator
Iterator iterate;
iterate = head_set.iterator();
// Displaying the tree set data
System.out.println("The resultant values till head set: ");
// Iterating through the headSet
while (iterate.hasNext()) {
// Printing the elements
System.out.println(iterate.next() + " ");
}
}
}
Output:
The resultant values till head set:
2
9
10
15
16
20
例 2-B:
Java 语言(一种计算机语言，尤用于创建网站)
// Java code to illustrate headSet() method of TreeSet class
// In an unsorted treeset but with String type elements
// Importing required classes
import java.io.*;
import java.util.Iterator;
import java.util.TreeSet;
// Main class
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an empty TreeSet
TreeSet<String> tree_set = new TreeSet<String>();
// Adding the elements using add()
tree_set.add("Welcome");
tree_set.add("To");
tree_set.add("Geek");
tree_set.add("4");
tree_set.add("Geeks");
tree_set.add("TreeSet");
// Creating the headSet tree
TreeSet<String> head_set = new TreeSet<String>();
// Limiting the values till 5
head_set = (TreeSet<String>)tree_set.headSet("To");
// Creating an Iterator
Iterator iterate;
iterate = head_set.iterator();
// Displaying the tree set data
System.out.println(
"The resultant values till head set: ");
// Iterating through the headSet
while (iterate.hasNext()) {
// Printing elements using next() method
System.out.println(iterate.next() + " ");
}
}
}
Output:
The resultant values till head set:
4
Geek
Geeks
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