Java--一些小实例

1、请设计一个方法，可以实现获取任意范围内的随机数。

package homeworkTwelve;import java.util.Scanner;public class SuiJiShu {public static void main(String[] args) {    Scanner sc=new Scanner(System.in);    System.out.println("请输入一个范围的最大值：");    int s1=sc.nextInt();    System.out.println("请输入一个范围的最小值：");    int s3=sc.nextInt();    int s2=zuizhongzhi(s1,s3);    System.out.println(s2);}public static int zuizhongzhi(int j,int k){    int x=(int)((Math.random()*(j-k)+k));    return x;}}

2、集合的嵌套遍历
需求：
我们班有学生，每一个学生是不是一个对象。所以我们可以使用一个集合表示我们班级的学生。ArrayList
但是呢，我们旁边是不是还有班级，每个班级是不是也是一个ArrayList。
而我现在有多个ArrayList。也要用集合存储，怎么办呢?

这是主方法：

package jihe;import java.util.ArrayList;import java.util.Iterator;public class First {public static void main(String[] args) {    ArrayList list=new ArrayList();    ArrayList list1=new ArrayList();    ArrayList list2=new ArrayList();    Student s1=new Student(20,"小华");    Student s2=new Student(22,"小明");    Student s3=new Student(24,"二狗子");    Student s4=new Student(21,"李建仁");    Student s5=new Student(23,"丢疯子");    Student1 c1=new Student1(20,"陈诺");    Student1 c2=new Student1(22,"姜泥");    Student1 c3=new Student1(24,"杨柳");    Student1 c4=new Student1(25,"梅月");    Student1 c5=new Student1(23,"代红");    list1.add(s1);    list1.add(s2);    list1.add(s3);    list1.add(s4);    list1.add(s5);    list.add(list1);    list2.add(c1);    list2.add(c2);    list2.add(c3);    list2.add(c4);    list2.add(c5);    list.add(list2);     Iterator it = list.iterator();     //班级1     if (it.hasNext()) {        System.out.println(it.next());    }    //班级2     if (it.hasNext()) {        System.out.println(it.next());    }}}

班级一：

package jihe;public class Student {private int age;private String name;public Student() {    super();}public Student(int age, String name) {    super();    this.age = age;    this.name = name;}public int getAge() {    return age;}public void setAge(int age) {    this.age = age;}public String getName() {    return name;}public void setName(String name) {    this.name = name;}@Overridepublic String toString() {    return "Stuent [age=" + age + ", name=" + name + "]";}}

班级二：

package jihe;public class Student1 {private int age;private String name;public Student1() {    super();}public Student1(int age, String name) {    super();    this.age = age;    this.name = name;}public int getAge() {    return age;}public void setAge(int age) {    this.age = age;}public String getName() {    return name;}public void setName(String name) {    this.name = name;}@Overridepublic String toString() {    return "Student1 [age=" + age + ", name=" + name + "]";}}

3、获取10个1-20之间的随机数，要求不能重复

package suijishutwo;import java.util.ArrayList;import java.util.Collection;import java.util.Iterator;public class SuiJiShuTwo {public static void main(String[] args) {    Collection sc=new ArrayList();    while(sc.size()!=10) {        int x=(int)(Math.random()*20+1);        if(!sc.contains(x)){            sc.add(x);        }    }    Iterator it=sc.iterator();    while (it.hasNext()) {        System.out.println(it.next());    }}}

4、使用ArrayList集合存储自定义对象并遍历(三种方式去实现)

package bianli;import java.util.ArrayList;import java.util.Collection;import java.util.Iterator;public class BianLi {public static void main(String[] args) {    Collection c=new ArrayList();    c.add("小明");    c.add("小华");    c.add("杨柳");    Object[] obj=c.toArray();    for (int i = 0; i < obj.length; i++) {        System.out.print(obj[i]);        System.out.print(" ");    }    System.out.println("");    Iterator it=c.iterator();    while(it.hasNext()){        System.out.print(it.next());        System.out.print(" ");    }    System.out.println("");    for (int i = 0; i < c.size(); i++) {        ArrayList c1=(ArrayList)c;        System.out.print(c1.get(i));        System.out.print(" ");    }}}