Java中各种集合判空方法总结

import org.springframework.util.CollectionUtils;

List<String> list = new ArrayList<>();

// 使用CollectionUtils判断list是否为空
if (!CollectionUtils.isEmpty(list)) {
    System.out.println("list is not empty");
}

List<String> list = new ArrayList<>();

if (list!=null && list.size()>0) {
    System.out.println("list is not empty");
}

List<String> list = new ArrayList<>();

if (list.isEmpty()) {
    System.out.println("list is empty");
}

List<String> list = new ArrayList<>();

if(StringUtils.isNull(list) || list.size() == 0){
  System.out.println("list is empty");
}

Object[] arr = new Object[0];
if (arr.length == 0) {
    System.out.println("数组为空");
}

Object[] arr = null;
if (arr == null) {
    System.out.println("数组为空");
}

Object[] arr = new Object[0];
if (arr == null || arr.length == 0) {
    System.out.println("数组为空");
}

Object[] arr1 = new Object[0];
if (Objects.isNull(arr1)) {
    System.out.println("数组为null");
}

Object[] arr2 = new Object[0];
if (Objects.nonNull(arr2)) {
    System.out.println("数组不为null");
}

public static void main(String[] args) {
    List list1 = new ArrayList();
    List list2 = null;
    System.out.println("结果1:" + CollectionUtils.isEmpty(list1));
    System.out.println("结果2:" + CollectionUtils.isEmpty(list2));
    System.out.println("结果3:" + list1.isEmpty());
    System.out.println("结果4:" + list2.isEmpty());
}