为什么这段使用多个构造函数的 Java 代码在 VS 代码中运行但不能用 javac 编译？

Question

我一直在尝试在 Java 中使用多个构造函数。 下面是我的代码：

public class MultipleConstructors {
    int x = 20;
    int y = 50;
    String color = "Green";
    String color2 = "Yellow";

    public MultipleConstructors() {

    }

    public MultipleConstructors(int numb, int numb2, String colOne, String colTwo) {
        x = numb;
        y = numb2;
        color = colOne;
        color2 = colTwo;
    }

    public MultipleConstructors(int numb3, int numb4, String colThree, String colFour) {
        x = numb3;
        y = numb4; 
        color = colThree;
        color2 = colFour;
    }

    public MultipleConstructors(int numb5, int numb6, String colFive, String colSix) {
        x = numb5;
        y = numb6; 
        color = colFive;
        color2 = colSix;
    }

    public static void main(String[] args) {
        MultipleConstructors myObjOne = new MultipleConstructors(100, 200, "Pink", "Blue");
        MultipleConstructors myObjTwo = new MultipleConstructors(300, 500, "Burgandy", "Silver");
        MultipleConstructors myObjThree = new MultipleConstructors(800, 1000, "Black", "White");
        MultipleConstructors myObjFour = new MultipleConstructors();

        System.out.println(myObjOne.x + myObjOne.y + " " + myObjOne.color + " " + myObjTwo.color2 + " " + " : SUCCESS");

        System.out.println(myObjTwo.x + myObjTwo.y + " " + myObjTwo.color + " " + myObjTwo.color2 + " " + " : VICTORY");

        System.out.println(myObjThree.x + myObjThree.y + " " + myObjThree.color + " " + myObjThree.color2 + " " + " : YES");

        System.out.println(myObjFour.x + myObjFour.y + " " + myObjFour.color + " " + myObjFour.color2 + " " + " : YES");
    }
}

它在 VS Code 中运行，但不会使用javac命令进行javac 。 我认为它可能是父属性声明之后未定义的构造函数public MultipleConstructors() {} 。

Answer 1

如果您收到类似以下错误消息的信息：

MultipleConstructors.java:11: error: constructor MultipleConstructors(int,int,java.lang.String,java.lang.String) is already defined in class MultipleConstructors

那么你应该使用这个答案。 如果您遇到 ClassNotFoundException，您应该看到 Ntshembo Hlongwane 的回答。

您的问题是您有多个相同的构造函数。 我认为你想要的是构造函数重载，这意味着你可以有多个具有不同标题的构造函数，但是你的三个构造函数具有相同的标题。 在下面的构造函数中查看我的评论：

public MultipleConstructors() {
    // header has no parameters
    // fine, leaves values alone
}

public MultipleConstructors(int numb, int numb2, String colOne, String colTwo) {
    // header has parameters int, int String String
    //fine, offers you the opportunity to change those values

    x = numb;
    y = numb2;
    color = colOne;
    color2 = colTwo;
}

public MultipleConstructors(int numb3, int numb4, String colThree, String colFour) {
    // header has parameters int, int, String, String
    // Wait, that's the same as the one above!

    x = numb3;
    y = numb4; 
    color = colThree;
    color2 = colFour;
}

public MultipleConstructors(int numb5, int numb6, String colFive, String colSix) {
    // header has parameters int, int, String, String
    // Wait, that's also the same as the one above!

    x = numb5;
    y = numb6; 
    color = colFive;
    color2 = colSix;
}

当您实例化这个对象，并给它两个整数和一个字符串时，您希望调用哪个构造函数？ 这是一个逻辑错误，而不是语法错误或编译器错误，因为您的代码有歧义。 希望这会有所帮助，并祝您在学习过程中取得成功。 :)

Answer 2

基于运行代码时发现的异常

Correct, runs in VSCode but won't compile in order to run in terminal. It throws the error "could not find or load main class " caused by "ClassNotFoundException"

这是由以下原因引起的：

• 假设您将文件命名为Test.java
• 然后在您的代码中，您将类编写为MyTest
• 当您尝试运行代码java Test您会收到以下错误：

Error: Could not find or load main class Test
Caused by: java.lang.ClassNotFoundException: Test

• 这是因为 Java 现在创建了一个MyTest.class ，你必须运行它