从列表容器中删除空值的 Java 程序
列表是对象的有序集合，允许按照插入顺序存储重复值或空值。因此，在许多情况下移除空值非常重要。
示例:
Input: [Geeks, null, forGeeks, null, A computer portal]
Output: [Geeks, forGeeks, A computer portal]
Input: [1, null, 2, 3, null, 4]
Output: [1, 2, 3, 4]
以下是在 Java 中从列表中移除空值的方法:
-
Using List.remove() List interface provides a pre-defined method remove(element) which is used to remove a single occurrence of the element passed, from the List, if found.
算法:
- 获取具有空值的列表。
- 重复调用列表中的移除(空)，直到所有空值都被移除。
- 返回/打印列表(现在删除所有空值)。
```java // Java Program to remove nulls // from a List using List.remove()
import java.util.*;
class GFG { public static void main(String[] args) {
// Create the list with null values List list = new ArrayList<>( Arrays.asList("Geeks", null, "forGeeks", null, "A computer portal"));
// Print the list System.out.println("Initial List: " + list);
// Removing nulls using List.remove() // Repeatedly call remove() till all null are removed while (list.remove(null)) { }
// Print the list System.out.println("Modified List: " + list); } } ```
Output:
```java Initial List: [Geeks, null, forGeeks, null, A computer portal] Modified List: [Geeks, forGeeks, A computer portal]
```
-
Using List.removeAll(): List interface provides another pre-defined method removeAll(Collection) which is used to remove all occurrences of the elements of the Collection passed, from the List, if found.
算法:
- 获取具有空值的列表。
- 使用 Collections.singletonList(空)创建一个只包含空元素的集合
- 调用列表中的移除所有(集合)一次。
- 返回/打印列表(现在删除所有空值)。
```java // Java Program to remove nulls // from a List using List.removeAll()
import java.util.*;
class GFG { public static void main(String[] args) {
// Create the list with null values List list = new ArrayList<>( Arrays.asList("Geeks", null, "forGeeks", null, "A computer portal"));
// Print the list System.out.println("Initial List: " + list);
// Removing nulls using List.removeAll() // passing a collection with single element "null" list.removeAll(Collections.singletonList(null));
// Print the list System.out.println("Modified List: " + list); } } ```
Output:
```java Initial List: [Geeks, null, forGeeks, null, A computer portal] Modified List: [Geeks, forGeeks, A computer portal]
```
-
Using iterator: Iterator is an interface which belongs to collection framework. It allows user to traverse the collection, access the data element and remove the data elements of the collection.
算法:
- 获取具有空值的列表。
- 从列表中创建迭代器
- 使用创建的迭代器遍历列表的每个元素
- 检查每个元素是否为空。如果发现为空，对该元素调用 IteratorElement.remove() 。
- 返回/打印列表(现在删除所有空值)。
程序:
```java // Java Program to remove nulls // from a List using iterator
import java.util.*;
class GFG {
// Generic function to remove Null Using Iterator public static List removeNullUsingIterator(List list) {
// Create an iterator from the list Iterator itr = list.iterator();
// Find and remove all null while (itr.hasNext()) { if (itr.next() == null) itr.remove(); // remove nulls }
// Return the null return list; }
public static void main(String[] args) {
// Create the list with null values List list = new ArrayList<>( Arrays.asList("Geeks", null, "forGeeks", null, "A computer portal"));
// Print the list System.out.println("Initial List: " + list);
// Removing nulls using iterator list = removeNullUsingIterator(list);
// Print the list System.out.println("Modified List: " + list); } } ```
Output:
```java Initial List: [Geeks, null, forGeeks, null, A computer portal] Modified List: [Geeks, forGeeks, A computer portal]
```
-
Using Guava Iterables removeIf(): Guava Iterables class provides Iterables.removeIf(Iterable, Predicate) that removes every element from a specified Iterable (or Collections that implements Iterable) that satisfies the provided predicate.
算法:
- 获取具有空值的列表。
- 获取谓词条件谓词. isNull() 以传入 removeIf()的参数
- 调用 Iterables.removeIf(List，谓词)其中 List 是带有空值的原始列表，谓词是谓词. isNull()实例。
- 返回/打印列表(现在删除所有空值)。
```java // Java Program to remove nulls // from a List using Guava Iterables
import com.google.common.base.Predicates; import com.google.common.collect.Iterables; import java.util.*;
class GFG { public static void main(String[] args) {
// Create the list with null values List list = new ArrayList<>( Arrays.asList("Geeks", null, "forGeeks", null, "A computer portal"));
// Print the list System.out.println("Initial List: " + list);
// Removing nulls using Guava Iterables // using Predicate condition isNull() Iterables.removeIf(list, Predicates.isNull());
// Print the list System.out.println("Modified List: " + list); } } ```
Output:
```java Initial List: [Geeks, null, forGeeks, null, A computer portal] Modified List: [Geeks, forGeeks, A computer portal]
```
-
Using Apache Commons Collections filter(): Apache Commons Collections CollectionUtils class provides filter(Iterable, Predicate) that removes every element from a specified iterable that do not satisfies the provided predicate.
算法:
- 获取具有空值的列表。
- 获取谓词条件谓词. NotNull 谓词()以传入 filter()的参数，这样通过条件 NotNull 的元素将保留在列表中，而所有其他元素都将被过滤。
- 调用 CollectionUtils.filter(list，predicteutils . not nullpredicate())其中 list 是带有空值的原始列表，predicteutils . not nullpredicate()实例是谓词。
- 返回/打印列表(现在删除所有空值)。
程序:
```java // Java Program to remove nulls // from a List using Apache Common COllection Filter() import org.apache.commons.collections4.CollectionUtils; import org.apache.commons.collections4.PredicateUtils; import java.util.*;
class GFG { public static void main(String[] args) {
// Create the list with null values List list = new ArrayList<>( Arrays.asList("Geeks", null, "forGeeks", null, "A computer portal"));
// Print the list System.out.println("Initial List: " + list);
// Removing nulls using Apache Common filter() // using Predicate condition notNullPredicate() CollectionUtils.filter(list, PredicateUtils.notNullPredicate());
// Print the list System.out.println("Modified List: " + list); } } ```
Output:
```java Initial List: [Geeks, null, forGeeks, null, A computer portal] Modified List: [Geeks, forGeeks, A computer portal]
```
-
Using Lambdas (Java 8): Stream.filter() method can be used in Java 8 that returns a stream consisting of the elements that match the given predicate condition.
算法:
- 获取具有空值的列表。
- 使用列表从列表中创建一个流
- 使用列表过滤不为空的元素流。= null)
- 使用将流作为列表收集回来。collect(Collectors.toList()
- 返回/打印列表(现在删除所有空值)。
```java // Java Program to remove nulls // from a List using Apache Common COllection Filter()
import java.util.stream.Collectors; import java.util.*;
class GFG { public static void main(String[] args) {
// Create the list with null values List list = new ArrayList<>( Arrays.asList("Geeks", null, "forGeeks", null, "A computer portal"));
// Print the list System.out.println("Initial List: " + list);
// Removing nulls using Java Stream // using Predicate condition in lambda expression list = list.stream() .filter(x -> x != null) .collect(Collectors.toList());
// Print the list System.out.println("Modified List: " + list); } } ```
Output:
```java Initial List: [Geeks, null, forGeeks, null, A computer portal] Modified List: [Geeks, forGeeks, A computer portal]
```
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