java - 返回 2 个不同的字符串

Question

是否可以执行此代码尝试执行的操作(当前代码格式导致错误)

public String fileStream(){
    Object[] yesNo = {"Yes",
          "No",};
int nn = JOptionPane.showOptionDialog(null,"Would you like to use previously entered data?","Welcome Back?",JOptionPane.YES_NO_OPTION,JOptionPane.QUESTION_MESSAGE, null, yesNo,yesNo[1]);
    if (nn == 0){
        String savedBallNumber = readFromFile();
        return savedBallNumber;
    }
    if (nn == 1){
        String ballNumber = JOptionPane.showInputDialog("Please enter the number of balls you want on the screen:");
        return ballNumber;
    }
}

当我将鼠标悬停在 fileStream 上时出现的错误是“此方法必须返回字符串类型的结果”

Answer 1

您的问题是您的代码在两个 if block 中返回，但没有 else block ，这意味着该方法有可能在不返回任何内容的情况下结束:

例如:

public String someMethod {
  if (a) {
    return "foo";
  }
  if (b) {
    return "bar";
  }
}

如果 a 和 b 都不为真，它返回什么。

解决方案:将最后一个 if block 更改为 else block :

public String fileStream() {
  Object[] yesNo = { "Yes", "No"};
  int nn = JOptionPane.showOptionDialog(null,
        "Would you like to use previously entered data?", "Welcome Back?",
        JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE, null,
        yesNo, yesNo[1]);
  if (nn == 0) {
     String savedBallNumber = readFromFile();
     return savedBallNumber;
  } else {
     String ballNumber = JOptionPane.showInputDialog("Please enter the number of balls you want on the screen:");
     return ballNumber;
  }
}