import java.util.*;

public class UpdateStu implements Comparable<Object> {

String name;

long id;

public UpdateStu(String name, long id) {

this.id = id;

this.name = name;

}

public int compareTo(Object o) {

UpdateStu upstu = (UpdateStu) o;

int result = id > upstu.id ? 1 : (id == upstu.id ? 0 : -1);

return result;

}

public long getId() {

return id;

}

public void setId(long id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public static void main(String[] args) {

UpdateStu stu1 = new UpdateStu("李同学", 01011);

UpdateStu stu2 = new UpdateStu("陈同学", 01021);

UpdateStu stu3 = new UpdateStu("王同学", 01051);

UpdateStu stu4 = new UpdateStu("马同学", 01012);

TreeSet<UpdateStu> tree = new TreeSet<>();

tree.add(stu1);

tree.add(stu2);

tree.add(stu3);

tree.add(stu4);

Iterator<UpdateStu> it = tree.iterator();

System.out.println("Set集合中的所有元素：");

while (it.hasNext()) {

UpdateStu stu = (UpdateStu) it.next();

System.out.println(stu.getId() + " " + stu.getName());

}

it = tree.headSet(stu2).iterator();

System.out.println("截取前面部分的集合：");

while (it.hasNext()) {

UpdateStu stu = (UpdateStu) it.next();

System.out.println(stu.getId() + " " + stu.getName());

}

it = tree.subSet(stu2, stu3).iterator();

System.out.println("截取中间部分的集合");

while (it.hasNext()) {

UpdateStu stu = (UpdateStu) it.next();

System.out.println(stu.getId() + " " + stu.getName());

}

}

}

为什么这段代码的ID都是01011这之类的数字，最后输出出来的结果都是三位数的呢。