这些都比较简单，首先来个多重if

package hjk;
import java.util.Scanner;
public class ojbk {
	public static void main(String[] args) {
		Scanner input=new Scanner(System.in);	
		System.out.print("韩嫣获得的名次为：");
		int a=input.nextInt();
		if(a<=1) {
			System.out.print("参加麻省理工大学组织的1个月夏令营");
		}else if(a<=2) {
			System.out.print("奖励惠普笔记本电脑一部");
		}else if(a<=3) {
			System.out.print("奖励移动硬盘一个");
		}else {
			System.out.print("无奖励");
		}
	}

}

学了switch，拿来试试

ackage hjk;
import java.util.Scanner;
public class obkii {
	public static void main(String[] args) {
		Scanner input=new Scanner(System.in);	
		System.out.print("韩嫣获得的名次为：");
		int a=input.nextInt();
		switch (a) {
		case 1:
			System.out.print("参加麻省理工大学组织的1个月夏令营");
			break;
		case 2:
			System.out.print("奖励惠普笔记本电脑一部");
			break;
		case 3:
			System.out.print("奖励移动硬盘一部");
			break;
		default:
			System.out.print("无奖励");
			break;
		
		}
	}
}