从列表中删除满足Java中给定谓词的元素

以下是从满足 Predicate 条件的 List 中有效删除元素的方法：

p  ==> Predicate, specifying the condition
l  ==> List, from which element to be removed

使用迭代器

下面的程序演示了使用 Predicate 从列表中删除空元素

Java

// 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  List
    removeNullUsingIterator(List l, Predicate p)
    {
 
        // Create an iterator from the l
        Iterator 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 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 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);
    }
}

输出

List with null values: [Geeks, null, forGeeks, null, A computer portal]
List with null values removed: [Geeks, forGeeks, A computer portal]

使用 List.removeAll()

在此方法中，包含要删除的元素的集合用于从原始 l 中删除这些元素。它需要使用 Predicate 条件创建包含所需元素的集合。完成此操作后，将在原始 l 中搜索此集合并删除它的所有实例。

Java

// 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  List
    removeElements(List l, Predicate p)
    {
 
        // Create collection using Predicate
        Collection 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 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 is10 = i -> (i == "10");
 
        // Removing using Predicate
        l = removeElements(l, is10);
 
        // Print the list
        System.out.println("Updated List: " + l);
    }
}

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]

使用 Lambda (Java 8)

Stream.filter() 方法可以在Java 8 中使用，它返回一个由元素组成的流
匹配给定的谓词条件。

Java

// 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  List
    removeElements(List l, Predicate 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 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 isNull = i -> (i != null);
 
        // Removing using Predicate
        l = removeElements(l, isNull);
 
        // Print the list
        System.out.println("List with null values removed: " + l);
    }
}

输出

List with null values: [Geeks, null, forGeeks, null, A computer portal]
List with null values removed: [Geeks, forGeeks, A computer portal]

使用 removeIf()

顾名思义，这是一种删除所有满足给定谓词的元素的直接方法。

Java

// 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  List
    removeElements(List l, Predicate 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 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 isNull = i -> (i == null);
 
        // Removing using Predicate
        l = removeElements(l, isNull);
 
        // Print the list
        System.out.println("List with null values removed: " + l);
    }
}

输出

List with null values: [Geeks, null, forGeeks, null, A computer portal]
List with null values removed: [Geeks, forGeeks, A computer portal]