utils014_拆分一个大集合为多个小集合

package com.itjingsong.test;

import com.google.common.collect.Lists;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
 * @author jingsong
 * @date 2022/6/6 22:06
 * @desc 业务有时需要对一个大集合拆分成多个小集合，介绍一种简单的工具类
 * 	<!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
 */
public class ListsTest {


    public static void main(String[] args) {

        List<String> list = Arrays.asList("aa", "bb", "cc", "dd", "ee");
        List<List<String>> lists1 = Lists.partition(list, 2);
        System.out.println("lists1 = " + lists1);
        List<List<String>> lists2 = Lists.partition(list, 3);
        System.out.println("lists2 = " + lists2);
        List<List<String>> lists3 = Lists.partition(list, 200);
        System.out.println("lists3 = " + lists3);

        List<String> strings = trimList(list, 3);
        System.out.println(list);
        System.out.println("strings = " + strings);

    }


    /**
     *  缩减集合的尺寸
     * @param list 目标集合
     * @param size 缩减到的尺寸
     * @param <T> 类型
     * @return 缩减后的尺寸
     */
    @SuppressWarnings("unchecked")
    public static <T> List<T> trimList(List<T> list, int size) {
        int num;
        if (list == null || (num = list.size()) == 0){
            return Collections.emptyList();
        }

        if (num <= size) {
            return list;
        }
        T[] ts = (T[]) Arrays.copyOf(list.toArray(), size);
        return Arrays.asList(ts);
    }
    
}