集合框架（上）：学生选课（collection）

利用集合存储课程信息：

1.Course类

package com.collection;

public class Course {
    public String id;
    public String name;
    public Course(String id,String name)
    {
        this.id=id;
        this.name=name;
    }

}

2.ListTest类

package com.collection;

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

/**
 * 备选课程类
*/

public class ListTest {
    //List用于存放备选课程
    public List CourseToSelect;
    public ListTest(){
        this.CourseToSelect = new ArrayList();
    }
    //用于往CourseToSelect添加备选课程
    public void TestAdd(){
        //创建一个课程对象，并通过调用add方法，添加到备选课程List中
        Course c1 = new Course("1","数据结构");
        CourseToSelect.add(c1);
        Course temp = (Course) CourseToSelect.get(0);
        System.out.println("添加了课程:"+temp.id+"_"+temp.name);

        Course c2 = new Course("2","c语言");
        CourseToSelect.add(0, c2);
        Course temp2 = (Course) CourseToSelect.get(0);
        System.out.println("添加了课程:"+temp2.id+"_"+temp2.name);

        Course[] course = {new Course("3","离散数学"),new Course("4","汇编语言")};
        CourseToSelect.addAll(Arrays.asList(course));
        Course temp3 = (Course) CourseToSelect.get(2);
        Course temp4 = (Course) CourseToSelect.get(3);
        System.out.println("添加了两门课程:"+temp3.id+"_"+temp3.name+";"+temp4.id+"_"+temp4.name);

        CourseToSelect.add(c1);
        Course temp0 = (Course) CourseToSelect.get(0);
        System.out.println("添加了课程:"+temp0.id+"_"+temp0.name);

        Course[] course2 = {new Course("5","高等数学"),new Course("6","大学英语")};
        CourseToSelect.addAll(2, Arrays.asList(course2));
        Course temp5 = (Course) CourseToSelect.get(2);
        Course temp6 = (Course) CourseToSelect.get(3);
        System.out.println("添加了两门课程:"+temp5.id+"_"+temp5.name+";"+temp6.id+"_"+temp6.name);

    }
    //取得List中元素的方法
    public void testGet(){
        int size = CourseToSelect.size();
        System.out.println("有如下课程待选：");
        for(int i = 0;i<size;i++)
        {
            Course cr = (Course) CourseToSelect.get(i);
            System.out.println("课程："+cr.id+":"+cr.name);
        }
    }
    //通过迭代器遍历List中的元素
    public void testIterator(){
        //通过集合的iterator方法，取得迭代器的实例；
        Iterator it = CourseToSelect.iterator();
        System.out.println("有如下课程待选(通过迭代器取得)：");
        while(it.hasNext()){
            Course cr2 = (Course) it.next();
            System.out.println("课程："+cr2.id+":"+cr2.name);
        }

    }
    //通过for each遍历list中的元素
    public void testForEach(){
        System.out.println("有如下课程待选(通过for each取得)：");
        for(Object obj:CourseToSelect){
            Course cr = (Course) obj;
            System.out.println("课程："+cr.id+":"+cr.name);

        }

    }

    //修改List中的元素
    public void testModify(){
        CourseToSelect.set(6, new Course("7","毛概"));

    }

    //删除List中的元素
    public void testRemove(){
        /*Course cr = (Course) CourseToSelect.get(6);
        System.out.println("课程："+cr.id+":"+cr.name+"我即将被删除");
        CourseToSelect.remove(cr);  //删除具体的元素*/
        //CourseToSelect.remove(4);  //删除索引4位置上的元素
        Course[] courses = {(Course)CourseToSelect.get(4),(Course)CourseToSelect.get(5)};
        CourseToSelect.removeAll(Arrays.asList(courses));
        System.out.println("成功被删除");
        testForEach();
    }

    public static void main(String[] args){
        ListTest lt = new ListTest();
        lt.TestAdd();
        lt.testGet();
        lt.testIterator();
        lt.testForEach();
        lt.testModify();
        lt.testForEach();
        lt.testRemove();
    }

}

3.testGeneric类

package com.collection;

import java.util.ArrayList;
import java.util.List;

public class TestGeneric {

    /**
     * @param args
     */
    //带有泛型List--course的类型属性
    public List<Course> courses;

    public TestGeneric(){
        this.courses=new ArrayList<Course>();
    }

    //测试添加
    public void testAdd(){
        Course cr1 = new Course("1","大学语文");
        courses.add(cr1);
        courses.add("平常的字符串");
    }
    public static void main(String[] args) {
        // TODO 自动生成的方法存根

    }

}

courses.add("平常的字符串")  编译器报错，因为泛型对规定了类型必须是course类型的元素

泛型例子

1.TestGeneric类

package com.collection;

import java.util.ArrayList;
import java.util.List;

public class TestGeneric {

    /**
     * @param args
     */
    //带有泛型List--course的类型属性
    public List<Course> courses;

    public TestGeneric(){
        this.courses=new ArrayList<Course>();
    }

    //测试添加
    public void testAdd(){
        Course cr1 = new Course("1","大学语文");
        courses.add(cr1);
        //泛型集合中，不能添加泛型规定的类型以及子类型以外的对象，否则编译器报错
        //courses.add("平常的字符串");
        Course cr2 = new Course("2","java基础");
        courses.add(cr2);

    }

    //泛型集合可以添加泛型子类型的对象实例
    public void testChild(){
        ChildCourse ccr = new ChildCourse();
        ccr.id="3";
        ccr.name="我是子类型的课程对象实例 ";
        courses.add(ccr);
    }

    //泛型不能使用基本类型
    public void testBasicType(){
        List<Integer> list = new ArrayList<Integer>();
        list.add(1);
        System.out.println("基本类型必须使用包装类作为泛型~~"+list.get(0));
    }

    //测试方法
    public void testForEach(){
        for(Course cr:courses){
            System.out.println(cr.id+":"+cr.name);
        }
    }
    public static void main(String[] args) {
        // TODO 自动生成的方法存根
        TestGeneric tg = new TestGeneric();
        tg.testAdd();
        tg.testForEach();
        tg.testChild();
        tg.testForEach();
        tg.testBasicType();

    }

}

2.ChildCourse继承Course类（在建立类中选择超类Course中即可）

package com.collection;

public class ChildCourse extends Course {

}

建立继承类只是为了验证泛型中可以添加子类型的对象实例

学生手动选课，显示学生的选课信息

1.student类

package com.collection;

import java.util.HashSet;
import java.util.Set;

/**
 * @学生类
 *
 */

public class Student {

    public String id;
    public String name;
    public Set<Course> courses;
    public Student(String id,String name)
    {
        this.id=id;
        this.name=name;
        this.courses=new HashSet<Course>();
    }

}

2.SetTest类

package com.collection;

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

public class SetTest {

    /**
     * @param args
     */

    public List<Course> CourseToSelect;
    public SetTest(){
        CourseToSelect = new ArrayList<Course>();
    }

    //添加元素
    public void TestAdd(){
        //创建一个课程对象，并通过调用add方法，添加到备选课程List中
        Course c1 = new Course("1","数据结构");
        CourseToSelect.add(c1);
        Course temp = (Course) CourseToSelect.get(0);
        //System.out.println("添加了课程:"+temp.id+"_"+temp.name);

        Course c2 = new Course("2","c语言");
        CourseToSelect.add(0, c2);
        Course temp2 = (Course) CourseToSelect.get(0);
        //System.out.println("添加了课程:"+temp2.id+"_"+temp2.name);

        Course[] course = {new Course("3","离散数学"),new Course("4","汇编语言")};
        CourseToSelect.addAll(Arrays.asList(course));
        Course temp3 = (Course) CourseToSelect.get(2);
        Course temp4 = (Course) CourseToSelect.get(3);
        //System.out.println("添加了两门课程:"+temp3.id+"_"+temp3.name+";"+temp4.id+"_"+temp4.name);

        //CourseToSelect.add(c1);
        //Course temp0 = (Course) CourseToSelect.get(0);
        //System.out.println("添加了课程:"+temp0.id+"_"+temp0.name);

        Course[] course2 = {new Course("5","高等数学"),new Course("6","大学英语")};
        CourseToSelect.addAll(2, Arrays.asList(course2));
        Course temp5 = (Course) CourseToSelect.get(2);
        Course temp6 = (Course) CourseToSelect.get(3);
        //System.out.println("添加了两门课程:"+temp5.id+"_"+temp5.name+";"+temp6.id+"_"+temp6.name);

    }

    //测试For Each打印输出
    public void testForEach(){
        System.out.println("有如下课程待选(通过for each取得)：");
        for(Object obj:CourseToSelect){
            Course cr = (Course) obj;
            System.out.println("课程："+cr.id+":"+cr.name);

        }

    }
    public static void main(String[] args) {
        // TODO 自动生成的方法存根
        SetTest st = new SetTest();
        st.TestAdd();
        st.testForEach();

        Student student = new Student("1","小明");
        System.out.println("欢迎同学："+student.name+"选课！");
        //创建Scanner对象，用于从键盘中输入课程的ID；
        Scanner console = new Scanner(System.in);
        for(int i=0;i<3;i++){
            System.out.println("输出课程ID");
            String courseId=console.next();
            for (Course cr : st.CourseToSelect) {
                if(cr.id.equals(courseId)){
                    student.courses.add(cr);
                }
            }
        }
        st.testForEachForSet(student);

    }

    // 打印输出，学生所选的课程
    public void testForEachForSet(Student student){
        for (Course cr : student.courses) {
            System.out.println("选择了课程:"+cr.id+":"+cr.name);

        }
    }

}

注：Set中，添加某个对象，无论添加多少次，最终只会保留一个该对象（的引用），并且，保留的事第一次添加的那个。

添加了两次课程1 但是最后的结果就是选择了两门课程。