package Dec2016; import java.util.ArrayList; import java.util.List; public class Ques1229 { public static void main(String[] args){ Student stu01 = new Student("001"); Student stu02 = new Student(null); List<Student> students = new ArrayList<Student>(); students.add(stu01); students.add(stu02); System.out.println("students是否包含001學號:"+students.contains(stu01)); System.out.println("students是否包含null:"+students.contains(stu02)); } } class Student{ private String stuId; public Student(String stuId) { super(); this.stuId = stuId; } public String getStuId() { return stuId; } public void setStuId(String stuId) { this.stuId = stuId; } @Override public boolean equals(Object obj) { if(obj instanceof Student){ Student stu = (Student) obj; return stuId.equalsIgnoreCase(stu.getStuId().trim()); } return false; } }今日問題: