Java determines whether a variable is empty

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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