注意移除null元素是修改List本身還是,生成新的List沒有null元素.

package com.sheting.basic.collection.list;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;

import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.collections4.PredicateUtils;

import com.google.common.base.Predicates;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;

public
 
 class RemoveNullsElement {

    public static void main(String[] args) {
        removeNullElement_1();
        removeNullElement_2();
        removeNullElement_3();
        removeNullElement_4();
        removeNullElement_5();
        removeNullElement_6();
        removeNullElement_7();
    }

    // **** Remove nulls from a List Using Plain Java
 

    public static void removeNullElement_1() {
        // UnsupportedOperationException
        // List<String> list = Arrays.asList(null, "china", null);

        List<String> list = new ArrayList<>();
        list.add(null);
        list.add("china");
        list.add(null);
        list
 
.removeAll(Collections.singleton(null));
        System.out.println(list); // [china]
    }

    public static void removeNullElement_2() {
        List<String> list = new ArrayList<>();
        list.add(null);
        list.add("china");
        list.add(null);
        while (list.remove(null))
            ;
        System.out.println(list); // [china]
    }

    // ****Remove nulls from a List Using Google Guava
    public static void removeNullElement_3() {
        List<String> list = Lists.newArrayList(null, "china", null);
        Iterables.removeIf(list, Predicates.isNull());
        System.out.println(list); // [china]
    }

    public static void removeNullElement_4() {
        List<String> list = Lists.newArrayList(null, "china", null);
        List<String> listWithoutNulls = Lists.newArrayList(Iterables.filter(list, Predicates.notNull()));
        System.out.println(list); // [null, china, null]
        System.out.println(listWithoutNulls); // [china]
    }

    // **** Remove nulls from a List Using Apache Commons Collections
    public static void removeNullElement_5() {
        List<String> list = Lists.newArrayList(null, "china", null);
        CollectionUtils.filter(list, PredicateUtils.notNullPredicate());
        System.out.println(list); // [china]
    }

    // ****Remove nulls from a List Using Lambdas (Java 8)
    public static void removeNullElement_6() {
        List<String> list = Lists.newArrayList(null, "china", null);
        List<String> listWithoutNulls = list.stream().filter(Objects::nonNull).collect(Collectors.toList());
        System.out.println(listWithoutNulls); // [china]
    }

    public static void removeNullElement_7() {
        List<String> list = Lists.newArrayList(null, "china", null);
        list.removeIf(Objects::isNull);
        System.out.println(list); // [china]
    }

}

output

[china]
[china]
[china]
[null, china, null]
[china]
[china]
[china]
[china]