极客教程Java 从List中删除满足给定谓词的元素
以下是有效地从满足谓词条件的列表中删除元素的方法：
p ==> 谓词，指定条件。
l ==> 列表，要从其中删除的元素。
使用迭代器
下面的程序演示了从列表中删除空元素，使用谓词
// Java Program to remove nulls
// from a List using iterator and Predicate
import java.util.function.Predicate;
import java.util.*;
class GFG {
// Generic function to remove Null Using Iterator
public static <T> List<T>
removeNullUsingIterator(List<T> l, Predicate<T> p)
{
// Create an iterator from the l
Iterator<T> itr = l.iterator();
// Find and remove all null
while (itr.hasNext()) {
// Fetching the next element
T t = itr.next();
// Checking for Predicate condition
if (!p.test(t)) {
// If the condition matches,
// remove that element
itr.remove();
}
}
// Return the null
return l;
}
public static void main(String[] args)
{
// Create the l with null values
List<String> l = new ArrayList<>(
Arrays.asList("Geeks",
null,
"forGeeks",
null,
"A computer portal"));
// Print the list
System.out.println("List with null values: " + l);
// Creating a Predicate condition checking for null
Predicate<String> isNull = item -> Objects.nonNull(item);
// Removing nulls using iterator and Predicate
l = removeNullUsingIterator(l, isNull);
// Print the list
System.out.println("List with null values removed: " + l);
}
}Java
输出
List with null values: [Geeks, null, forGeeks, null, A computer portal]
List with null values removed: [Geeks, forGeeks, A computer portal]Java
时间复杂度：O(N^2 )
空间复杂度。O(N)
使用List.removeAll()
在这个方法中，一个包含要删除的元素的集合被用来从原始l中删除这些元素。它需要使用一个Predicate条件创建一个包含所需元素的集合。做完这些后，原始的l被搜索到这个集合，并且所有的实例都被删除。
// Java Program to remove 10
// from a List using List.removeAll() and Predicate
import java.util.function.Predicate;
import java.util.*;
class GFG {
// Generic function to remove elements using Predicate
public static <T> List<T>
removeElements(List<T> l, Predicate<T> p)
{
// Create collection using Predicate
Collection<T> collection = new ArrayList<>();
for (T t : l) {
if (p.test(t)) {
collection.add(t);
}
}
// Print the list
System.out.println("Collection to be removed: " + collection);
// Removing 10 using List.removeAll()
// passing a collection
l.removeAll(collection);
// Return the list
return l;
}
public static void main(String[] args)
{
// Create a list with null values
List<String> l = new ArrayList<>(
Arrays.asList("1", "10", "15", "10", "12", "5", "10", "20"));
// Print the list
System.out.println("Original List: " + l);
// Creating a Predicate condition checking for 10
Predicate<String> is10 = i -> (i == "10");
// Removing using Predicate
l = removeElements(l, is10);
// Print the list
System.out.println("Updated List: " + l);
}
}Java
输出
Original List: [1, 10, 15, 10, 12, 5, 10, 20]
Collection to be removed: [10, 10, 10]
Updated List: [1, 15, 12, 5, 20]Java
使用Lambdas (Java 8)
在Java 8中可以使用Stream.filter()方法，该方法返回一个由符合给定谓词条件的元素组成的流 。
// Java Program to remove nulls
// from a List using Java 8
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.*;
class GFG {
// Generic function to remove elements using Predicate
public static <T> List<T>
removeElements(List<T> l, Predicate<T> p)
{
// Removing nulls using Java Stream
// using Predicate condition in lambda expression
l = l.stream()
.filter(p)
.collect(Collectors.toList());
// Return the list
return l;
}
public static void main(String[] args)
{
// Create a list with null values
List<String> l = new ArrayList<>(
Arrays.asList("Geeks",
null,
"forGeeks",
null,
"A computer portal"));
// Print the list
System.out.println("List with null values: " + l);
// Creating a Predicate condition checking for null
Predicate<String> isNull = i -> (i != null);
// Removing using Predicate
l = removeElements(l, isNull);
// Print the list
System.out.println("List with null values removed: " + l);
}
}Java
输出
List with null values: [Geeks, null, forGeeks, null, A computer portal]
List with null values removed: [Geeks, forGeeks, A computer portal]Java
使用removeIf()
顾名思义，它是一个直接删除所有满足给定谓词的元素的方法。
// Java Program to remove nulls
// from a List using Java 8
import java.util.function.Predicate;
import java.util.*;
class GFG {
// Generic function to remove elements using Predicate
public static <T> List<T>
removeElements(List<T> l, Predicate<T> p)
{
// Removing nulls using Java Stream
// using Predicate condition in removeIf()
l.removeIf(x -> p.test(x));
// Return the list
return l;
}
public static void main(String[] args)
{
// Create a list with null values
List<String> l = new ArrayList<>(
Arrays.asList("Geeks",
null,
"forGeeks",
null,
"A computer portal"));
// Print the list
System.out.println("List with null values: " + l);
// Creating a Predicate condition checking for null
Predicate<String> isNull = i -> (i == null);
// Removing using Predicate
l = removeElements(l, isNull);
// Print the list
System.out.println("List with null values removed: " + l);
}
}Java
输出
List with null values: [Geeks, null, forGeeks, null, A computer portal]
List with null values removed: [Geeks, forGeeks, A computer portal]Java