Java-11.4/11.5作业

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。

package org.lemon.Test;

import java.util.Random;

public class TestDemo {
public static void main(String[] args) {
int max = 100;
int min = 1;
//创建Random对象
Random random = new Random();
//定义一个数
int a = random.nextInt(max)%(max-min+1)+min;

System.out.println(a);

}
}

2:下面代码执行的结果是:    false   true

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));
}

}

3:下面代码执行的结果是:      AB    B

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;
}

4、下列代码的执行结果是：   str1 == This is a test!Hi      str2 == This is a test!Hi

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);

5:下面代码能最后打印的值是?   D

    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）nullC）0        
D）1

编程题

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<Student>

  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<Student>。

  而我现在有多个ArrayList<Student>。也要用集合存储，怎么办呢?

  

package org.lemon.Test;
import java.util.ArrayList;
public class TestDemo {
public static void main(String[] args) {
ArrayList<ArrayList<Student>> big = new ArrayList<ArrayList<Student>>();
//一个
ArrayList<Student> a = new ArrayList<Student>();
Student s1 = new Student ("kobe",1);
Student s2 = new Student ("james",2);
Student s3 = new Student ("brown",3);
Student s4 = new Student ("tt",4);

a.add(s1);
a.add(s2);
a.add(s3);
a.add(s4);
big.add(a);
//另一个
ArrayList<Student> b = new ArrayList<Student>();
Student s5 = new Student ("nash",5);
Student s6 = new Student ("fisher",6);
Student s7 = new Student ("odom",7);
Student s8 = new Student ("buynm",8);
b.add(s5);
b.add(s6);
b.add(s7);
b.add(s8);
big.add(b);

for(ArrayList<Student>array : big) {
for(Student s :array) {
System.out.println(s.getAge()+"----"+s.getName());
}
}
}
}

package org.lemon.Test;

public class Student {
private String name ;
private int age ;

public Student() {
super();
}
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}

@Override
public String toString() {
return "Student [name=" + name + ", age=" + age + "]";
}
}

2:获取10个1-20之间的随机数，要求不能重复

package org.lemon.Test;

import java.util.ArrayList;
import java.util.Random;

public class TestDemo {
public static void main(String[] args) {

ArrayList <Integer>  array = new ArrayList<Integer>();

//创建Random对象
Random random = new Random();
int count = 0;
while(count<10) {
int number = random.nextInt(20)+1;
if(!array.contains(number){
array.add(number);
count++;
}
}
for(Integer i : array) {
System.out.println(i);
}

}
}

3:使用ArrayList集合存储自定义对象并遍历(三种方式去实现)

package org.lemon.List;
//用List集合存储字符串类型的元素,并遍历:迭代器遍历
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class ListDemo {
public static void main(String[] args) {
List list = new ArrayList();

list.add("我");
list.add("爱");
list.add("你");

Iterator it = list.iterator();
while(it.hasNext()) {
String s = (String) it.next();
System.out.println(s);
}
}
}

//for的方法遍历list集合,使用size()和get()相结合
for(int  x = 0 ; x < list.size(); x ++){
Object object = list.get(x) ;
//获取字符串内容同时,获取字符串长度
String s = (String)list.get(x) ;
System.out.println(s+"----"+s.length());
}

//获取列表迭代器
ListIterator it = list.listIterator() ;
while(it.hasNext()){
String s = (String) it.next();
System.out.println(s);

}