public class Program4 {
    static StringBuffer str = new StringBuffer();
    
    public static void main(String[] args) {
        System.out.print(test(90));
    }
    
    public static String test(int n) {
        str = str.append(n+ " = 1");
        if(n <= 3) {
            System.out.print("请输入一个大于3的正整数！");
            System.exit(1);    
        }
            
        for(int i = 2; i <= n; i++) {
            if(n%i == 0) {
                str = str.append("*" +i);
                n = n/i;
                return test1(n);
            }
        }
        return " errer";
    }
    public static String test1(int n) {
        for(int i = 2; i <= n; i++) {
            if(n%i == 0) {
                str = str.append("*" +i);
                n = n/i;
                if(n == 1) {
                    return str.toString();
                }
                return test1(n);
            }
        }
        return "err";
    }
    
}

public class Program4 {
    static StringBuffer str = new StringBuffer();

    private static boolean first = true;

    public static void main(String[] args) {
        System.out.print(test(90));
    }

    public static String test(int n) {

        if (first) {
            str = str.append(n + " = 1 ");

            if (n <= 3) {

                System.out.print("请输入一个大于3的正整数！");
                System.exit(1);
            }
        }

        first = false;

        if (n == 1)
            return str.toString();

        for (int i = 2; i <= n; i++) {
            if (n % i == 0) {
                str = str.append("* " + i);
                n = n / i;
                return test(n);
            }
        }

        return " errer";
    }

}

------解决方案--------------------
Java code
public class Program4 {
    static StringBuffer str = new StringBuffer();
    
    public static void main(String[] args) {
        System.out.print(test2(200));
    }
    
    public static String test(int n) {
        str = str.append(n+ " = 1");
        if(n <= 3) {
            System.out.print("请输入一个大于3的正整数！");
            System.exit(1);    
        }
            
        for(int i = 2; i <= n; i++) {
            if(n%i == 0) {
                str = str.append("*" +i);
                n = n/i;
                return test1(n);
            }
        }
        return " errer";
    }
    public static String test1(int n) {
        for(int i = 2; i <= n; i++) {
            if(n%i == 0) {
                str = str.append("*" +i);
                n = n/i;
                if(n == 1) {
                    return str.toString();
                }
                return test1(n);
            }
        }
        return "err";
    }
    
    //下面的test2不用递归：
    //
    public static String test2(int n){
        if(n<=3){
            System.out.print("请输入一个大于3的正整数！");
            System.exit(1); 
        }
        str.append(n+" = 1");
        int x=n;
        int i=2;
        while(x!=1){
            if(x%i==0){
                str.append("*"+i);
                x/=i;
            }else{
                i++;
            }
        }
        return str.toString();
    }
    
}