java作业

1: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?
创建学生类

public class Student {    private int age;    private String 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;    }    public Student(int age, String name) {        super();        this.age = age;        this.name = name;    }    @Override    public String toString() {        return "Student [age=" + age + ", name=" + name + "]";    }}

import java.util.ArrayList;import java.util.Iterator;public class ArrayListDemo {    public static void main(String[] args) {        ArrayList class1=new ArrayList();        Student s1=new Student(20, "paul");        Student s2=new Student(20, "kobe");        Student s3=new Student(20, "james");        Student s4=new Student(20, "allen");        class1.add(s1);        class1.add(s2);        class1.add(s3);        class1.add(s4);        ArrayList class2=new ArrayList();        Student s5=new Student(20, "paul1");        Student s6=new Student(20, "kobe2");        Student s7=new Student(20, "james3");        Student s8=new Student(20, "allen4");        class2.add(s8);        class2.add(s7);        class2.add(s6);        class2.add(s5);        ArrayList school=new ArrayList();        school.add(class1);        school.add(class2);        Iterator it=school.iterator();        while(it.hasNext()) {            Object s= it.next();            System.out.println(s);        }        }}

2:获取10个1-20之间的随机数，要求不能重复

import java.util.Scanner;import java.util.Random;public class SuiJiShu {          public static void main(String[] args){          Scanner sc=new Scanner(System.in);          System.out.println("请输入你想获取多少以内的随机值");          int index=sc.nextInt();          Random r=new Random();          int a=r.nextInt(index+1);          System.out.println("你获得的随机值为:"+a);          }        }

3:使用ArrayList集合存储自定义对象并遍历(三种方式去实现)

import java.util.ArrayList;import java.util.Iterator;public class ArrayListDemo1 {        public static void main(String[] args) {            Student s1= new Student(20,"paul");            Student s2= new Student(20,"answer");            ArrayList al=new ArrayList();            al.add(s1);            al.add(s2);            //方法1                    Iterator it=al.iterator();                    System.out.print("[");                    while(it.hasNext()) {                        System.out.print(it.next()+", ");                    }                    System.out.println("]");                    //方法二                    Object[] arr=al.toArray();                    for(int i=0;i<arr.length;i++) {                    System.out.print(arr[i]+", ");                    }                    System.out.println();                    //方法三                    while(it.hasNext()) {                        Student a=(Student)it.next();                        System.out.print(a+",  ");                    }                }        }

1:需求：请设计一个方法，可以实现获取任意范围内的随机数。

public class RandeomDemo{  public static void main(String[] args){  Scanner sc=new Scanner(System.in);  System.out.println("请输入你想获取多少以内的随机值");  int index=sc.nextInt();  Random r=new Random();  int a=r.nextInt(index+1);  System.out.println("你获得的随机值为："+a);  }}

2:下面代码执行的结果是:
public static void main(String[] args) {
String s1 = new String(“hello”);
String s2 = new String(“hello”);
System.out.print(s1 == s2);
System.out.print(“,”);
System.out.println(s1.equals(s2));
}
}

false,ture

3:下面代码执行的结果是:
public static void main(String arg[]) {
StringBuffer a = new StringBuffer(“A”);
StringBuffer b = new StringBuffer(“B”);
operate(a, b);
System.out.println(a + “,” + b);
}
static void operate(StringBuffer x, StringBuffer y) {
x.append(y);
y = x;
}

AB,B

4:下面代码执行的结果是
6、下列代码的执行结果是：
String str1 = “This is a test!”;
StringBuffer str2 =new StringBuffer( “This is a test!”);
str1 = str1+”Hi”;
str2.append(“Hi”);
System.out.println(“str1 == ” + str1);
System.out.println(“str2 == ” + str2);

This is a Text!HiThis is a Text!Hi

7:下面代码能最后打印的值是?
public class TestValue {
private static int a;

public static void main(String[] args) {    modify(a);    System.out.println(a);}public static void modify(int a) {    a++;}

}
A）编译错误 B）null C）0 D）1

C