空指针异常

package imooc_collection_lesson;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.Scanner;

public class SetTest {

private static final List<Course> coursesToSelect = null;

public List<Course> coursesToCourses;

public SetTest(){

coursesToCourses=new ArrayList<Course>();

}

public void TestAdd(){

//创建一个课程对象，并通过add方法，添加到备选课程中去

Course cou1=new Course("1","数据结构");

coursesToCourses.add(cou1);

Course Temp=(Course)coursesToCourses.get(0);

//System.out.println("添加了一个课程:"+Temp.id+":"+Temp.name);

Course cou2=new Course("2", "C语言");

coursesToCourses.add(0,cou2);

Course Temp2=(Course)coursesToCourses.get(0);

//System.out.println("添加了一个课程:"+Temp2.id+":"+Temp2.name);

//以下方法会抛出数组下标越界异常

/* Course cou3=new Course("3", "大学英语");

courseToSelect.add(4,cou3);

*/

//Course cou3=new Course("1", "数据结构");

//courseToSelect.add(2,cou3);

Course[] course={new Course("3","离散数学"),

new Course("4","汇编语言")};

coursesToCourses.addAll(Arrays.asList(course));

Course Temp3=(Course) coursesToCourses.get(2);

Course Temp4=(Course) coursesToCourses.get(3);

//System.out.println("添加了两门课程："+Temp3.id+":"+Temp3.name

// +Temp4.id+":"+Temp4.name);

Course[] course2={new Course("5","高等数学"),

new Course("6","大学体育")};

coursesToCourses.addAll(2,Arrays.asList(course2));

Course Temp5=(Course) coursesToCourses.get(2);

Course Temp6=(Course) coursesToCourses.get(3);

//System.out.println("添加了两门课程："+Temp5.id+":"+Temp5.name

// +Temp6.id+":"+Temp6.name);

}

public void testForEach(){

System.out.println("有如下课程待选(通过for each访问)：");

for(Object obj:coursesToCourses){

Course sr=(Course) obj;

System.out.println("课程："+sr.id+";"+sr.name);

}

}

/**

 * 测试List的contains方法

 */

public void testListContains() {

// 取得备选课程序列的第0个元素

Course course = coursesToSelect.get(0);

// 打印输出coursesToSelected是否包含course对象

System.out.println("取得课程：" + course.name);

System.out.println("备选课程中是否包含课程：" + course.name + ", " + 

coursesToSelect.contains(course));

}

public static void main(String[] args) {

// TODO Auto-generated method stub

SetTest st=new SetTest();

st.TestAdd();

st.testListContains();

}

public void testForEachForSet(Student student)

{

for (Course sr : student.Courses) {

System.out.println("选择了课程："+sr.id+":"+sr.name);

    }

}

}

执行时报错Exception in thread "main" java.lang.NullPointerException at imooc_collection_lesson.SetTest.testListContains(SetTest.java:67) at imooc_collection_lesson.SetTest.main(SetTest.java:77)