添加到ArrayList

Question

我无法弄清楚为什么我无法向ArrayList添加项目。我尝试了几种不同的方式添加项目，但它们不起作用。

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);

}

我也试过

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

这也不起作用。

编译器说预期标识符。

Answer 1

尝试将import java.util.ArrayList;添加到文件顶部。

您还需要运行main方法，其签名如下：

public static void main(String[] args)

另外，如果您不打算更改字符串常量final（和/或static），则应该使字符串常量{。

最后，temp1是默认（“朋友”）可见性。

我假设这是一个代码片段，而不是你实际运行的代码片段。

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

实际上，你错过了方法声明。

尝试将代码放在Main方法中：

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


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

  }
}