This is the 19th day of my participation in the Gwen Challenge in November. Check out the details: The last Gwen Challenge in 2021

Lists are often manipulated in real development, and null-nulling is often required to avoid null-pointer exceptions. The general way to write this is:

if(the list! =null && list.size>0) {// Perform the set operation
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Method 1 (large amount of data, low efficiency) :if(list! =null && list.size()>0Method 2 (large amount of data, high efficiency) :if(list! =null && !list.isEmpty()){
}
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Look at the ArrayList source code below, don’t understand why the efficiency gap (just remember that for now, unfortunately).

    public int size(a) {
        return size;
    }

    public boolean isEmpty(a) {
        return size == 0;
    }
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Most frameworks provide a utility class like CollectionUtils

  1. For example, the Spring framework:

The package path is as follows:

package org.springframework.util.CollectionUtils;
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With utility classes, collection nulling is much simpler:

if(CollectionUtils.isEmpty()){
// The operation on the set
}
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  1. Another example is the Apache CollectionUtils utility class:

Maven coordinates:

<dependency>
            <groupId>commons-collections</groupId>
            <artifactId>commons-collections</artifactId>
            <version>3.22.</version>
</dependency>
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Package path:

package org.apache.commons.collections;
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With utility classes, collection nulling is much simpler:

if(CollectionUtils.isEmpty()){
// The operation on the set} orif(CollectionUtils.isNotEmpty()){
// The operation on the set
}
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Reference links: blog.csdn.net/z1573262158…