java删除list中所有null值
java Collection 框架提供简单解决方案,通过基本的while循环实现:
@Test
public void givenListContainsNulls_whenRemovingNullsWithPlainJava_thenCorrect() {
List<Integer> list = Lists.newArrayList(null, 1, null);
while (list.remove(null));
assertThat(list, hasSize(1));
}
remove方法当参数为null时,背后也是for循环,删除null 返回true,继续外层循环,直至全部null被删除。当然我们也可以使用removeAll方法
@Test
public void givenListContainsNulls_whenRemovingNullsWithPlainJavaAlternative_thenCorrect() {
List<Integer> list = Lists.newArrayList(null, 1, null);
list.removeAll(Collections.singleton(null));
assertThat(list, hasSize(1));
}
也可以通过Google Guava提供更实用的方法,使用predicte:
@Test
public void givenListContainsNulls_whenRemovingNullsWithGuavaV1_thenCorrect() {
List<Integer> list = Lists.newArrayList(null, 1, null);
Iterables.removeIf(list, Predicates.isNull());
assertThat(list, hasSize(1));
}
如果我们不想修改原list,可以创建一个新list
@Test
public void givenListContainsNulls_whenRemovingNullsWithGuavaV2_thenCorrect() {
List<Integer> list = Lists.newArrayList(null, 1, null, 2, 3);
List<Integer> listWithoutNulls = Lists.newArrayList(
Iterables.filter(list, Predicates.notNull()));
assertThat(listWithoutNulls, hasSize(3));
}
Apache Commons Collections提供了简单的方式实现,使用类似函数式编程方式
@Test
public void givenListContainsNulls_whenRemovingNullsWithCommonsCollections_thenCorrect() {
List<Integer> list = Lists.newArrayList(null, 1, 2, null, 3, null);
CollectionUtils.filter(list, PredicateUtils.notNullPredicate());
assertThat(list, hasSize(3));
}
java 8 lambda表达式解决方案,过滤list,且过滤过程可以是并行或串行:
@Test
public void givenListContainsNulls_whenFilteringParallel_thenCorrect() {
List<Integer> list = Lists.newArrayList(null, 1, 2, null, 3, null);
List<Integer> listWithoutNulls = list.parallelStream()
.filter(Objects::nonNull)
.collect(Collectors.toList());
}
@Test
public void givenListContainsNulls_whenFilteringSerial_thenCorrect() {
List<Integer> list = Lists.newArrayList(null, 1, 2, null, 3, null);
List<Integer> listWithoutNulls = list.stream()
.filter(Objects::nonNull)
.collect(Collectors.toList());
}
public void givenListContainsNulls_whenRemovingNullsWithRemoveIf_thenCorrect() {
List<Integer> listWithoutNulls = Lists.newArrayList(null, 1, 2, null, 3, null);
listWithoutNulls.removeIf(Objects::isNull);
assertThat(listWithoutNulls, hasSize(3));
}