数组合并：直接使用common-lang中的jar包
pom.xml配置

<dependency>
      <groupId>org.apache.commons</groupId>
      <artifactId>commons-lang3</artifactId>
      <version>3.7</version>
</dependency>

基本数据类型的排序不必重写compareTo方法

package ArrayDemo;

import org.apache.commons.lang3.ArrayUtils;

import java.util.Arrays;

public class ArrayMerge {

    public static void main(String[] args) {

        int i_first[] = {1,3,3,7};
        int i_second[] = {2,7,9};

        int contact[] = ArrayUtils.addAll(i_first, i_second);
        Arrays.sort(contact);

        for (int i:contact) {
            System.out.println(i + " ");
        }

    }
}

package ListDemo;

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

public class ListMerge {

    public static void main(String[] args) {
        List<Person> list_first = new ArrayList<>();
        List<Person> list_second = new ArrayList<>();
        List<Person> list_final = new ArrayList<>();

        Person p_one = new Person("Sandy",17);
        Person p_two = new Person("Monica",20);
        Person p_three = new Person("Coco", 16);
        Person p_four = new Person("Ivy", 18);

        list_first.add(p_one);
        list_first.add(p_two);

        list_second.add(p_three);
        list_second.add(p_four);

        list_final.addAll(list_first);
        list_final.addAll(list_second);

        /*
         * Object 排序一
         */
        Object[] obj = list_final.toArray();
        Arrays.sort(obj);
        for (Object o:obj) {
            System.out.println(((Person)o).getAge() +" ");
        }

        /*
         * Object 排序二
         * 调用原理：Collections类 ——> List的sort方法 ——> List的sort方法中调用toArray()——>调用数组的sort方法Array.sort()
         * ——> 调用compareTo()方法
         */
//        Collections.sort(list_final);
//        for (Person person : list_final) {
//            System.out.println( person.getAge() +" ");
//        }

    }

    public static class Person implements Comparable<Person>
    {
        private static final long serialVersionUID = 8656128222714547171L;
        transient private String name;
        private int age;

        Person(String name,int age){
            this.name= name;
            this.age=age;
        }

        public int getAge() {
            return age;
        }

        public String getName() {
            return name;
        }

        public void setAge(int age) {
            this.age = age;
        }

        public void setName(String name) {
            this.name = name;
        }

        @Override
        public int compareTo(Person o) {
            return (this.age < o.getAge()) ? -1 : ((this.age == o.getAge()) ? 0 : 1);
        }
    }

}