Question

我试图创建一个程序，使字符串s1等于某些文本，具体取决于hours变量。问题是当我运行程序时s1找不到。我刚刚开始使用Java，所以我不确定这是否真的效率低下，或者它是不是很简单，我不知道。

代码：

export default Vue.component('radioButton', {
  template,
  props: ['name', 'label', 'id', 'value']
})

Answer 1

变量的范围是声明变量的块。块从开口花括号开始，并在匹配的闭合花括号处停止。因此，您要声明三个不同的变量，这些变量在其块之外是不可见的（这就是为什么Java允许您使用相同的名称将其声明三次）。

在块之外声明变量一次：

String s1;
if (b5) {
    s1 = "You have played for " + arr[0] + " hours!";
}
...

Answer 2

试试这个..

int[] arr;
arr = new int[2];
arr[0] = 1;
boolean b1 = arr[0] > 1;
boolean b2 = arr[0] < 1;
boolean b4 = 0 > arr[0];
boolean b3 = b4 && b2;
boolean b5 = b1 || b3;
 String s1 = "";
if (b5) {
     s1 = "You have played for " + arr[0] + " hours!";

}
else if (arr[0] == 1) {
     s1 = "You have played for 1 hour!";

}
else if (arr[0] == 5) {
     s1 = "You have not played at all!";
}
else {
     s1 = "Memory Error in arr[0], Are the hours negative? Is it there?";
}
System.out.print (s1);
}

Answer 3

您需要在main方法的开头定义String s1，如下所示：

     String s1;

稍后，当您设置s1（在if，else语句中）时，您可以写：

     s1 = "You have played for......";

这样，s1将在代码的开头声明。

Answer 4

代码块内部发生了什么，保留在该代码块中。如果您在if block中声明变量，则if block之外的变量不可见 - 甚至不在else if和else个案例中。您的代码不应该编译，因为之前没有声明最后的s1。

    String s1;
    if (b5) {
       s1 = "You have played for " + arr[0] + " hours!";

    }
    else if (arr[0] == 1) {
       s1 = "You have played for 1 hour!";

    }
    else if (arr[0] == 5) {
       s1 = "You have not played at all!";
    }
    else {
       s1 = "Memory Error in arr[0], Are the hours negative? Is it there?";
    }
    System.out.print(s1);

这应该可以正常工作。

变量不是由if语句定义的

4 个答案: