Java 函数调用和声明

问：

我是 java 的新手，写关于将数字相加的代码，编写私有函数。我在未解析的变量上遇到错误，在标记上遇到错误，并且缺少构造。我不太确定出了什么问题。

import javax.swing.*;
    public class Note12FunctionExamples {
    int number1Integer = 0;
        int number2Integer = 0;
        int additionResultInteger = 0;
    
        number1Integer = 3;
        number2Integer = 4;
        
        
        additionResultInteger = addTwoNumbersAndReturnAdditionResult(number1Integer, number2Integer);
    outputMessageString = number1Integer + " + " + number2Integer + " is: " + additionResultInteger;
        JOptionPane.showMessageDialog(null, outputMessageString);

private static int addTwoNumbersAndReturnAdditionResult(int number1Integer, int number2Integer) {
        int additionResultInteger = 0;

        additionResultInteger = number1Integer + number2Integer;

        return additionResultInteger;
    }
}