Java中的 TreeSet subSet() 方法

Java.util.TreeSet.subSet() 用于返回参数中提到的范围内现有 TreeSet 的子集。该方法接受一个上限和一个下限，并返回范围内提到的所有元素。如果元素存在于集合中，则包括下限并且排除上限。基本上，它取大于等于下限且严格小于上元素的子集。

句法：

TreeSet tree_set.subSet(Object low_element, Object up_element)

范围：

• low_element：这是 TreeSet 的类型，定义了评估子集的下限或起始元素。该元素包含在子集中。
• up_element：这是 TreeSet 的类型，定义了评估子集的上限或最后一个元素。该元素被排除在子集中。

返回值：该方法返回给定参数范围内提到的 TreeSet 类型的子集。

下面的程序说明了Java.util.TreeSet.subSet() 方法：

程序 1 ：

// Java code to illustrate subSet() method
import java.io.*;
import java.util.Iterator;
import java.util.TreeSet;
  
public class Tree_Set_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty TreeSet
        TreeSet tree_set = new TreeSet();
  
        // Adding the elements using add()
        tree_set.add(5);
        tree_set.add(1);
        tree_set.add(50);
        tree_set.add(10);
        tree_set.add(20);
        tree_set.add(6);
        tree_set.add(20);
        tree_set.add(18);
        tree_set.add(9);
        tree_set.add(30);
  
        // Creating the subset tree
        TreeSet sub_set = new TreeSet();
  
        // Limiting the values till 5
        sub_set = (TreeSet)tree_set.subSet(6, 30);
  
        // Creating an Iterator
        Iterator iterate;
        iterate = sub_set.iterator();
  
        // Displaying the tree set data
        System.out.println("The resultant values within the sub set: ");
  
        // Iterating through the subset
        while (iterate.hasNext()) {
            System.out.println(iterate.next() + " ");
        }
    }
}

输出：

The resultant values within the sub set: 
6 
9 
10 
18 
20

方案二：

// Java code to illustrate subSet() method when TreeSet
// contains elements of String type
import java.io.*;
import java.util.Iterator;
import java.util.TreeSet;
  
public class Tree_Set_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty TreeSet
        TreeSet tree_set = new TreeSet();
  
        // 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 subset tree
        TreeSet sub_set = new TreeSet();
  
        // Limiting the values till 5
        sub_set = (TreeSet)tree_set.subSet("4", "TreeSet");
  
        // Creating an Iterator
        Iterator iterate;
        iterate = sub_set.iterator();
  
        // Displaying the tree set data
        System.out.println("The resultant values within the sub set: ");
  
        // Iterating through the subset
        while (iterate.hasNext()) {
            System.out.println(iterate.next() + " ");
        }
    }
}

输出：

The resultant values within the sub set: 
4 
Geek 
Geeks 
To