添加到ArrayList

Question

我不明白為什么不能將項目添加到ArrayList中。 我嘗試了幾種添加項目的方式，但它們不起作用。

class Problem {
public ArrayList<String> problems = new ArrayList<String>();
public ArrayList<String> answers = new ArrayList<String>();

private String question1 = "What is 2+2?";
private String question2 = "What is the square root of 25";
private String question3 = "What is the next number in the sequence? {2, 4, 6}";
private String question4 = "What is 8*8?";



String[] temp1 = {question1, question2, question3, question4};


for (String s : temp1)
    problems.add(s);

}

我也嘗試過

problems.add(question1);
problems.add(question2);
problems.add(question3);
problems.add(question4);

這也不起作用。

編譯器說該標識符是預期的。

Answer 1

嘗試添加import java.util.ArrayList; 到文件頂部。

您還需要運行一個main方法，其簽名如下：

public static void main(String[] args)

另外，如果您不打算更改字符串常量，則應該使它們成為final （和/或static ）。

最后， temp1是默認的（“朋友”）可見性。

我假設這是一個代碼段，而不是您實際運行的代碼段。

Answer 2

import java.util.ArrayList;

class Problem {

public static ArrayList<String> problems = new ArrayList<String>();
public static ArrayList<String> answers = new ArrayList<String>();

private static String question1 = "What is 2+2?";
private static String question2 = "What is the square root of 25";
private static String question3 = "What is the next number in the sequence? {2, 4, 6}"; 
private static String question4 = "What is 8*8?";

public static void main(String [] args) {

String[] temp1 = {question1, question2, question3, question4};


for (String s : temp1)
    problems.add(s);

System.out.println(""+problems);
}

}

Answer 3

實際上，您缺少方法聲明。

嘗試將代碼放入Main方法中：

public static void main(String[] args) {
  String[] temp1 = {question1, question2, question3, question4};


  for (String s : temp1)
      problems.add(s);

  }
}