当我没有 main 方法时，我的程序如何 运行

Question

我正在大学学习 java 课程，我们正在使用一个名为 acm 的库。但是当我们编写代码时，我们不会创建 main 方法。 "public void run(){}" 作为主要方法。请解释。

例如，这是我创建的一个程序。

import acm.program.ConsoleProgram;
import acm.util.RandomGenerator;

public class Assignment3 extends ConsoleProgram {

    private static final long serialVersionUID = 1L;
    private RandomGenerator rgen = RandomGenerator.getInstance();

    public void run() {
        final int QUESTION_AMOUNT = 5;

        println("Welcome to the Math Quiz! You have " + QUESTION_AMOUNT + " questions to answer! Good luck!");

        for (int i = 0; i < QUESTION_AMOUNT; i++) {
            askQuestion();
        }

        println("End of the quiz!");
    }

    public void askQuestion() {
        int num1, num2, kidanswer, realanswer;
        String operation = "";
        boolean x = rgen.nextBoolean();

        if (x == true) {
            operation = "+";
        } else {
            operation = "-";
        }

        if (operation == "-") {
            num1 = rgen.nextInt(0, 20);
            num2 = rgen.nextInt(0, num1);
        } else {
            num1 = rgen.nextInt(0, 20);
            num2 = rgen.nextInt(0, 20 - num1);
        }

        String question = ("What is " + num1 + " " + operation + " " + num2 + " = ");

        if (operation == "-") {
            realanswer = num1 - num2;
        } else {
            realanswer = num1 + num2;
        }

        kidanswer = readInt(question);

        int i = 0;
        while (i < 2) {
            if (kidanswer == realanswer) {
                println("That is correct! Well done!");
                break;
            } else {
                kidanswer = readInt("Wrong answer. Please try another answer: ");
                i++;
                if (i == 2) {
                    if (kidanswer == realanswer) {
                        println("That is correct! Well done!");
                    } else {
                        println("Sorry :( Out of tries! The answer was: " + realanswer);

                    }
                }
            }
        }
    }
}

Answer 1

Something 必须提供一个主要方法。在你的情况下，它几乎肯定会是你的 class 扩展的 ACM 东西（ConsoleProgram），并且在某些时候会调用你的 run 方法。

Answer 2

因为：

• Assignment3 extends ConsoleProgram
• ConsoleProgram extends Program
• Program defines main.