千峰逆战班，Day24

在千峰“逆战班”学习的第24天
今天的学习内容是泛型中的实例泛型，静态泛型以及Collections工具类
中国加油！武汉加油！千峰加油！我自己加油！！！

11.C
12.

public class Question {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入字符串长度：");
		int n = sc.nextInt();
		StringBuilder sb = new StringBuilder();
		java.util.Random r = new java.util.Random();
		//48~57 数字  大写：65~90 小写：97~122
		for(int i = 0; i < n; i++){
			int a = r.nextInt(62);
			if(a < 10){
				sb.append(a);
			}else if(a >= 10 && a < 36){
				sb.append((char) (a + 55));
			}else{
				sb.append((char)(a + 61));
			}
		}
		String str = sb.toString();
		System.out.println(str);
	}	
}

运行结果：

public class Question13 {
	public static void main(String[] args){
		Scanner sc1 = new Scanner(System.in);
		System.out.println("请输入一个字符串：");
		String str1 = sc1.next();
		System.out.println("请输入要查询的子串：");
		String str2 = sc1.next();
		System.out.println(str1.contains(str2));
	
		for(int i = 0; i < str1.length(); i++){
			int a = str1.indexOf(str2,i);
			if(a != -1){
				System.out.println(a);
				i = a;
			}
		}
	}
}

public class Question14 {
	public static void main(String[] args){
		List<Student> list = new ArrayList<Student>();
		list.add(new Student("Tom",18,100,"class05"));
		list.add(new Student("Jerry",22,70,"class04"));
		list.add(new Student("Owen",25,90,"class05"));
		list.add(new Student("Jim",30,80,"class05"));
		list.add(new Student("Steve",28,66,"class06"));
		list.add(new Student("Kevin",24,100,"class04"));
		int sum = 0;
		for(int i = 0; i <list.size(); i++){
			sum = sum + list.get(i).age;
		}
		int avgAge = sum / list.size();
		System.out.println(avgAge);
		double sum04 = 0;
		int count04 = 0;
		double sum05 = 0;
		int count05 = 0;
		double sum06= 0;
		int count06 = 0;
		
		for(int i = 0; i < list.size(); i++){
			if(list.get(i).classNum.equals("class05")){
				sum05 = sum05 + list.get(i).score;
				count05++;
			}else if(list.get(i).classNum.equals("class04")){
				sum04 = sum04 + list.get(i).score;
				count04++;
			}else{
				sum06 = sum06 + list.get(i).score;
				count06++;
			}
		}
		System.out.println("class04班的平均成绩为：" + sum04 / count04 );
		System.out.println("class05班的平均成绩为：" + sum05 / count05 );
		System.out.println("class06班的平均成绩为：" + sum06 / count06);
	}
}
class Student{
	String name;
	int age;
	double score;
	String classNum;
	public Student(){}
	public Student(String name,int age,double score,String classNum){
		this.name = name;
		this.age = age;
		this.score = score;
		this.classNum = classNum;
	}
}

运行结果: