How to determine whether a java object is empty

First let’s look at the judgment method of the tool StringUtils:

One is under the org.apache.commons.lang3 package; the other is org.springframework. Under the util package. There is a difference between these two StringUtils tool classes in determining whether an object is empty:

StringUtils.isEmpty(CharSequence cs); //org.apache.commons.lang3包下的StringUtils类，判断是否为空的方法参数是
字符序列类，也就是String类型
StringUtils.isEmpty(Object str); //而org.springframework.util包下的参数是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。

From the above example, we can see that the second StringUtils class is more practical.

Let’s take a look at the source code of StringUtils.isEmpty(CharSequence cs) of org.apache.commons.lang3:

public static boolean isEmpty(final CharSequence cs) {
    return cs == null || cs.length() == 0;
}

The next step is StringUtils.isEmpty(Object str) of org.springframework.util Source code:

public static boolean isEmpty(Object str) {
    return (str == null || "".equals(str));
}

Basically determine whether the object is empty, StringUtils.isEmpty(Object str) can do this.

The next step is to determine whether the array is empty

list.isEmpty(); //返回boolean类型。

Judge whether the set is empty

Example 1, determine whether the set 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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