java的集合嵌套及三种遍历

古城微笑少年丶 2022-07-13 11:48 196阅读 0赞

package exercise03_jdknews;
    
    import java.util.ArrayList;
    import java.util.Iterator;
    
    /**
     * 集合的嵌套 每个班级的学生 ArrayList<Student> 多个班级 ArrayList<ArrayList<Student>>
     * 
     * @author lgt
     *
     */
    public class CollectionNest {
        
        public static void main(String[] args) {
            // 创建大集合
            ArrayList<ArrayList<Student>> bigList = new ArrayList<ArrayList<Student>>();
    
            // 创建第一个班级的集合、学生
            ArrayList<Student> list1 = new ArrayList<Student>();
            Student s1 = new Student("hello1", 223);
            Student s2 = new Student("hello5", 93);
            Student s3 = new Student("hello23", 123);
            Student s4 = new Student("hello123", 999);
            Student s5 = new Student("hello222", 1992);
            //添加到第一个班级集合
            list1.add(s1);
            list1.add(s2);
            list1.add(s3);
            list1.add(s4);
            list1.add(s5);
    
            //添加班级到年级集合
            bigList.add(list1);
    
            // 创建第二个班级的集合、学生
            ArrayList<Student> list2 = new ArrayList<Student>();
            Student ss1 = new Student("java1", 1511);
            Student ss2 = new Student("java2", 1566);
            Student ss3 = new Student("java3", 1755);
            Student ss4 = new Student("java4", 1833);
            Student ss5 = new Student("java5", 1960);
            // 添加到第二个班级集合
            list2.add(ss1);
            list2.add(ss2);
            list2.add(ss3);
            list2.add(ss4);
            list2.add(ss5);
    
            //添加到年级集合
            bigList.add(list2);
    
            // 创建第一个班级的集合、学生
            ArrayList<Student> list3 = new ArrayList<Student>();
            Student sss1 = new Student("world10", 1990);
            Student sss2 = new Student("world12", 1990);
            Student sss3 = new Student("world15", 1995);
            Student sss4 = new Student("world19", 1998);
            Student sss5 = new Student("world20", 2006);
            // 添加到集合
            list3.add(sss1);
            list3.add(sss2);
            list3.add(sss3);
            list3.add(sss4);
            list3.add(sss5);
    
            //添加第三班级到年级集合
            bigList.add(list3);
    
            //遍历年级方式1 迭代器
            Iterator<ArrayList<Student>> it = bigList.iterator();
            int count1 = 1;
            while(it.hasNext()){
                System.out.println("班级" + count1);
                Iterator<Student> itt = it.next().iterator();
                while(itt.hasNext()){
                    Student s = itt.next();
                    s.show();
                }
                count1++;
            }
            System.out.println("----------------------");
    
            //遍历年级方式2 for
            int count2 = 1;
            for(int i = 0; i < bigList.size(); i++){
                System.out.println("班级" + count2);
                for(int j = 0; j < bigList.get(i).size(); j++){
                    Student s = bigList.get(i).get(j);
                    s.show();
                }
                count2++;
            }
            System.out.println("----------------------");
    
            //遍历方式3 增强for
            int count3 = 1;
            for(ArrayList<Student> i : bigList){
                System.out.println("班级" + count3);
                for(Student s : i){
                    s.show();
                }
                count3++;
            }
        }
    }