常用的静态引用

import static java.util.Collections.singletonList;
import static java.util.Collections.singletonMap;
import static java.util.Collections.singleton;
import static java.util.Collections.emptyList;
import static java.util.Collections.emptyMap;
import static java.util.Collections.emptySet;
import static java.util.stream.Collectors.*;
import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.tuple;
import static org.mockito.Mockito.when;
import static org.mockito.MockitoAnnotations.initMocks;