List segmentation best practices

Catalog

One ListUtils.partition Method

1.1  Introduce dependencies

1.2  Code demonstration

1.3 Output results

Two   Lists.partition Method

2.1 Introduce dependencies

2.2 Code demonstration

2.3 Output results

3、 ... and Source code analysis

3.1 ListUtils.partition Source code analysis

3.2 Lists.partition Source code analysis

Four Performance comparison

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In our work, we often encounter the need to divide the array into multiple sub arrays , Then the demand for batch processing . Is there a more elegant implementation ？

After many times of practice , Sum up ListUtils.partition and Lists.partition Two better implementations . The two implementations are described below .

One ListUtils.partition Method

1.1  Introduce dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-collections4</artifactId>
    <version>4.4</version>
</dependency>

1.2  Code demonstration

public static void main(String[] args) {
    // Initialize array 
    List<Integer> parList = new ArrayList<>();
    IntStream.range(0, 30).forEach(parList::add);

    // Split into subarrays 
    List<List<Integer>> subList = ListUtils.partition(parList, 10);

    // Traversal subarray 
    subList.forEach(list -> {
        System.out.println(String.format("subList size:%s", list.size()));
        System.out.println(String.format("list:%s", list.toString()));
    });
}

1.3 Output results

Two   Lists.partition Method

2.1 Introduce dependencies

<dependency>
	<groupId>com.google.guava</groupId>
	<artifactId>guava</artifactId>
	<version>29.0-jre</version>
</dependency>

2.2 Code demonstration

public static void main(String[] args) {
    // Initialize array 
    List<Integer> parList = new ArrayList<>();
    IntStream.range(0, 30).forEach(parList::add);

    // Split into subarrays 
    List<List<Integer>> subList = Lists.partition(parList, 10);

    // Traversal subarray 
    subList.forEach(list -> {
        System.out.println(String.format("subList size:%s", list.size()));
        System.out.println(String.format("list:%s", list.toString()));
    });
}

2.3 Output results

3、 ... and Source code analysis

3.1 ListUtils.partition Source code analysis

Final ListUtils.partition call  ListUtils.Partition Method to handle .

ListUtils.Partition Source code is as follows ：

Partition Class as  ListUtils Static inner class inheritance AbstractList class . Rewrote get and size Method .

3.2 Lists.partition Source code analysis

Lists.partition The method will eventually be called new Partition<>(list, size).

Partition Class source code is as follows ：

Partition Class as  Lists Static inner class inheritance AbstractList class . Rewrote get 、 size、isEmpty Method .

Four Performance comparison

because Lists.partition and ListUtils.partition The underlying implementations are implemented through Partition Class to achieve , Similar performance .