java determines whether a variable is empty
1. Determine whether a string or object is empty
Let’s take a look first How to judge the tool StringUtils:
a) StringUtils under the org.apache.commons.lang3 package
StringUtils.isEmpty(CharSequence cs); // 判断是否为空的方法参数是字符序列类,也就是String类型
b) StringUtils
StringUtils.isEmpty(Object str); //参数是Object类,也就是不仅仅能判断String类型,还能判断其他类型,比如Long等类型。
under the org.springframework.util package From the above example, we can see that the second StringUtils class is more practical.
2. Determine whether the array is empty
list.isEmpty(); //返回boolean类型。
3. Determine whether the set is empty
Example 1: Determine the set Whether it is empty:
CollectionUtils.isEmpty(null): true CollectionUtils.isEmpty(new ArrayList()): true CollectionUtils.isEmpty({a,b}): false
Example 2: Determine whether the set is not empty:
CollectionUtils.isNotEmpty(null): false CollectionUtils.isNotEmpty(new ArrayList()): false CollectionUtils.isNotEmpty({a,b}): true
Operation between 2 sets:
Set a: {1,2,3 ,3,4,5}
Set b: {3,4,4,5,6,7}
CollectionUtils.union(a, b)(并集): {1,2,3,3,4,4,5,6,7} CollectionUtils.intersection(a, b)(交集): {3,4,5} CollectionUtils.disjunction(a, b)(交集的补集): {1,2,3,4,6,7} CollectionUtils.disjunction(b, a)(交集的补集): {1,2,3,4,6,7} CollectionUtils.subtract(a, b)(A与B的差): {1,2,3} CollectionUtils.subtract(b, a)(B与A的差): {4,6,7}
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