用java实现几个简单的递归题目

public class Recursion {
	public static void main(String[] args) {
		Recursion re = new Recursion();
		
		//例题1 1到100内数的总和
		int value = re.getSum(100);
		System.out.println(value);
		
		//例题2 1到100内数的乘积:n!
		int value1 = re.getCheng(5);
		System.out.println(value1);
		
		//例题3 已知数列f(0) = 1,f(1) = 4,f(n+2) = 2*f(n+1) + f(n);求f(10);	
		int value2 = re.f(10);
		System.out.println(value2);
		
		//例题4 斐波那契数列 1 1 2 3 5 8 ... f(n) = f(n-1) + f(n-2);
		int value3 = re.ff(5);
		System.out.println(value3);
		
	}
	
	
	public int getSum(int n) {
			if(n == 1) {
				return 1;
			}else {
				return (n + getSum(n-1));
			}
	}
	
	public int getCheng(int n) {
		if(n == 1) {
			return 1;
		}else {
			return n * getCheng(n-1);
		}
	}
	
	public int f(int n) {
		if(n == 0) {
			return 1;
		}else if(n == 1) {
			return 4;
		}else {//必须向着已知的走将n+2看成N即可
			return  2 * f(n-1) + f(n-2);
		}
	}
	
	public int ff(int n) {
		if(n == 1 || n == 2) {
			return 1;
		}else {
			return ff(n-1) + ff(n-2);
		}
	}
}

运行结果：