从另一个类运行一个类的方法

Question

我的Java包中有四个类。 只有一个类具有main()方法。

当我运行main()方法时，如何在四个类中运行所有方法？

这是我的课程：

Cat1.java

package test;

public class Cat1 {

    public Cat1() {
        System.out.println("100");
    }

    public Cat1(int i ){
        i = 10;
        System.out.println(" cat1 i :"+ i);
    }
}

---

Cat2.java

package test;

public class Cat2 extends Cat1 {

    public Cat2() {
        System.out.println("200");
    }

    public Cat2(int i ){
        super();
        System.out.println("Cat 2 ; "+ i);
    }
}

---

Cat3.java

package test;

public class Cat3 extends Cat2{

    public Cat3() {
        System.out.println("300");
    }

    public Cat3(int i){
        super();
        System.out.println("Cat 3 : "+ i);
    }

}

---

Sample.java

package test;

import java.text.DateFormat;
import java.util.Calendar;
import java.util.Locale;

public class Sample {

    /**
     * @param args
     */
    public static void main(String[] args) {

        Calendar cal = Calendar.getInstance();

        //Date d = cal.getTime();
        Locale locale = new Locale("en");
        DateFormat dateFormat = DateFormat.getDateInstance(DateFormat.FULL, locale);
        System.out.println(" LONg date : " + dateFormat.format(cal.getTime()));

        String incomeData = "200,2,2,2,2";


        int expense = 0;
        String expenseSplit = incomeData;
        System.out.println(" e");
        String expenseArray[] = expenseSplit.split(",");
        String income = expenseArray[0];
        for (int i = 1; i < expenseArray.length; i++) {
            expense = expense+Integer.parseInt(expenseArray[i]);
        }
        System.out.println(" Income "+ income);
        System.out.println(" expense "+ expense);


    }

}

Answer 1

看起来您只是该对象的新对象，并调用了您需要的功能。
如

Cat3 cat3 = new Cat3();

还是要在main（）方法运行时自动调用它？

Answer 2

Java是一种面向对象的语言，因此，如果您不引用对象，它们只会坐在那里，什么也不做。 在main方法中，您可以将其视为可以创建对象并使用它们访问对象上的方法的起点。

在main（）方法内部，您可以只创建一些对象。

Cat1 sampleCat1 = new Cat1();
Cat1 anotherSampleCat1 = new Cat1(4);

Answer 3

package test;
import java.text.DateFormat;
import java.util.Calendar;
import java.util.Locale;

public class Sample {

    public static void main(String[] args) {
        Cat1 cat1 = new Cat1(1);
        Cat2 cat2 = new Cat2(2);
        Cat3 cat3 = new Cat3(3);
        Calendar cal = Calendar.getInstance();

        //Date d = cal.getTime();
        Locale locale = new Locale("en");
        DateFormat dateFormat = DateFormat.getDateInstance(DateFormat.FULL, locale);
        System.out.println(" LONg date : " + dateFormat.format(cal.getTime()));

        String incomeData = "200,2,2,2,2";


        int expense = 0;
        String expenseSplit = incomeData;
        System.out.println(" e");
        String expenseArray[] = expenseSplit.split(",");
        String income = expenseArray[0];
        for (int i = 1; i < expenseArray.length; i++) {
            expense = expense+Integer.parseInt(expenseArray[i]);
        }
        System.out.println(" Income "+ income);
        System.out.println(" expense "+ expense);

    }
}