Java TreeSet retainAll()用法及代碼示例

java.util.TreeSet類的retainAll()方法用於從該集合中保留指定集合中包含的所有元素。

用法:

public boolean retainAll(Collection c)

參數：此方法將集合c作為包含要從該集合保留的元素的參數。

返回值：如果此集合因調用而更改，則此方法返回true。

異常：如果此集合包含null元素並且指定的集合不允許null元素(可選)，或者指定的collection為null，則此方法引發NullPointerException。

以下示例說明了retainAll()方法。

示例1:

// Java program to demonstrate 
// retainAll() method for Integer value 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) throws Exception 
    { 
  
        try { 
  
            // Creating object of TreeSet<Integer> 
            TreeSet<Integer> 
                set1 = new TreeSet<Integer>(); 
  
            // Populating set1 
            set1.add(1); 
            set1.add(2); 
            set1.add(3); 
            set1.add(4); 
            set1.add(5); 
  
            // print set1 
            System.out.println("TreeSet before "
                               + "retainAll() operation : "
                               + set1); 
  
            // Creating another object of  TreeSet<Integer> 
            TreeSet<Integer> 
                set2 = new TreeSet<Integer>(); 
            set2.add(1); 
            set2.add(2); 
            set2.add(3); 
  
            // print set2 
            System.out.println("Collection Elements"
                               + " to be retained : "
                               + set2); 
  
            // Removing elements from set 
            // specified in set2 
            // using retainAll() method 
            set1.retainAll(set2); 
  
            // print set1 
            System.out.println("TreeSet after "
                               + "retainAll() operation : "
                               + set1); 
        } 
  
        catch (NullPointerException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

輸出：

TreeSet before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : [1, 2, 3]
TreeSet after retainAll() operation : [1, 2, 3]

示例2:對於NullPointerException

// Java program to demonstrate 
// retainAll() method for Integer value 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) throws Exception 
    { 
  
        try { 
  
            // Creating object of TreeSet<Integer> 
            TreeSet<Integer> 
                set1 = new TreeSet<Integer>(); 
  
            // Populating set1 
            set1.add(1); 
            set1.add(2); 
            set1.add(3); 
            set1.add(4); 
            set1.add(5); 
  
            // print set1 
            System.out.println("TreeSet before "
                               + "retainAll() operation : "
                               + set1); 
  
            // Creating another object of  TreeSet<Integer> 
            TreeSet<Integer> 
                set2 = null; 
  
            // print set2 
            System.out.println("Collection Elements"
                               + " to be retained : "
                               + set2); 
  
            System.out.println("\nTrying to pass "
                               + "null as a specified element\n"); 
  
            // Removing elements from set 
            // specified in set2 
            // using retainAll() method 
            set1.retainAll(set2); 
  
            // print set1 
            System.out.println("TreeSet after "
                               + "retainAll() operation : "
                               + set1); 
        } 
  
        catch (NullPointerException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

輸出：

TreeSet before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : null

Trying to pass null as a specified element

Exception thrown : java.lang.NullPointerException

相關用法

注：本文由純淨天空篩選整理自Code_r大神的英文原創作品 TreeSet retainAll() method in Java with Example。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。