java - 怎么输入回车跳出循环

Question

这是我上java课要做的题，我在这个直接按回车键结束循环这里困住了。

请问要怎么修改呢？谢谢！

System.out.println(" ==== 构建园对象并计算其面积周长 ==== ");
System.out.println("请输入半径（直接按回车键结束程序）");
while(true)
{
    circleANDrectangle a1 = new circleANDrectangle();
    if()
        break;
    else
        a1.radius = input.nextDouble();
    number++;
    System.out.println("构建了半径为"+a1.radius+"的园，圆面积"+
    a1.yuans()+"、周长"+a1.yuanc());
    System.out.println("目前园个数为"+number);
    System.out.println("请输入半径（直接按回车键结束程序）");
}
System.out.println("——程序结束。");`

Answer 1

public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    int count=0;
    while(true)
    {
        
        System.out.println("请输入半径：（直接按回车键程序结束）");
        String s = in.nextLine();
        if (s.equals("")){
            System.out.println("——————程序结束");
            break;
            }
        else{
            
            double r =Double.parseDouble(s);
            circle c = new circle(r);
            c.outValue();
            count++;
            System.out.println("目前圆个数:"+count);
        }
        
        
    }
}

This is a solution provided by a classmate, and it can be implemented.