JAVA 简单算法题 只能用 while if循环

这个算法题做不出来

要求是只能用while if循环
本人刚学不会做 希望有解答

public class ShowCube {

public static void showCubes(int lower,int upper){
    //循环结束标志
    boolean isEnd = false;
    boolean hasCube = false;
    //结果字符串
    StringBuilder sb = new StringBuilder();
    //循环初始值
    int currentNumber = lower;
    while(!isEnd){
        //计算立方
       int cube = currentNumber*currentNumber*currentNumber;
       if(cube>=lower&&cube<=upper){
           hasCube = true;
           sb.append(" ").append(currentNumber).append("^3=").append(cube).append(" <");
       } else if(cube>upper){
           isEnd = true;
       }
       currentNumber+=1;
       if(currentNumber>upper){
           break;
       }
    }
    if(hasCube){
        System.out.println("The cubes in["+lower+","+upper+"] are:");
        System.out.println(lower+" <="+sb.toString()+"= "+upper);
    } else{
        System.out.println("There are no cubes in["+lower+","+upper+"]");
    }
}


public static void main(String[] args) {
    showCubes(1,30);

    showCubes(10,20);
}

}