如何在Java中使用構造函數

Question

public class Person{

    public static void main(String[] args){
        //Class constructor
        Person(String name, String status, int Age){
            this.name = name;
            this.status = status;
            this.Age = Age;
        }
        //Object creation
        Person one = new Person("John", "Single", 18);
        Person two = new Person("Kez", "Single", 21);
        Person three = new Person("Bob", "Married", 31);

        //Print out attributes
        System.out.println("Person one Profile: %s/t%s/t%d", +one.name,    +one.status, +one.Age);
        System.out.println("Person two Profile: %s/t%s/t%d", +two.name, +two.status, +two.Age);
        System.out.println("Person three Profile: %s/t%s/t%d", +three.name, +three.status, +three.Age);
    }
}

我的代碼有什么問題？ 編譯器警告的錯誤並不能幫助我理解問題。

Answer 1

您的代碼有5個問題。 首先，變量應以小寫字母開頭，因此我將Age更改為age 。 其次，構造函數不應位於main方法中。 第三，您需要printf而不是println 。 另外，您還需要擺脫那些+號。 +是一個運算符，需要2個String （在任一側），而不僅僅是一個String 。 最后，我假設您的意思是\\t而不是/t 。 我已更改此設置，還添加了兩個換行符。

更正的代碼是

public class Person {

    private String name;
    private String status;
    private int age;

    Person(String name, String status, int age){
        this.name = name;
        this.status = status;
        this.age = age;
    }

    public static void main(String[] args) {
        //Object creation
        Person one = new Person("John", "Single", 18);
        Person two = new Person("Kez", "Single", 21);
        Person three = new Person("Bob", "Married", 31);

        //Print out attributes
        System.out.printf("Person one Profile: %s\t%s\t%d\n", one.name, one.status, one.age);
        System.out.printf("Person two Profile: %s\t%s\t%d\n", two.name, two.status, two.age);
        System.out.printf("Person three Profile: %s\t%s\t%d", three.name, three.status, three.age);
    }
}

Answer 2

構造函數是一種特殊的方法。 這些通常需要在其他方法之外。

//Class constructor
Person(String name, String status, int Age){
    this.name = name;
    this.status = status;
    this.Age = Age;
}
public static void main(String[] args){

  //Object creation
  Person one = new Person("John", "Single", 18);
  Person two = new Person("Kez", "Single", 21);
  Person three = new Person("Bob", "Married", 31);

  //Print out attributes
  System.out.println("Person one Profile: %s/t%s/t%d", +one.name,    +one.status, +one.Age);
  System.out.println("Person two Profile: %s/t%s/t%d", +two.name, +two.status, +two.Age);
  System.out.println("Person three Profile: %s/t%s/t%d", +three.name, +three.status, +three.Age);
}

默認情況下，構造函數在每個類中。 如果您的Person類中沒有constructuro，那么您將有一個默認值，因此您可以調用

new Person();

通過添加一個帶有string，string，int的構造函數，然后可以松開該默認構造函數。 如果您想要一個沒有輸入參數的默認值，那么您將需要再次添加它

Person(){}

Answer 3

嘗試這個：

class Test{
  public static void main(String[] args){

    //Object creation
    Person one = new Person("John", "Single", 18);
    Person two = new Person("Kez", "Single", 21);
    Person three = new Person("Bob", "Married", 31);

    //Print out attributes
    System.out.printf("Person one Profile:\t %s\t%s\t%d%n", one.name, one.status, one.age);
    System.out.printf("Person two Profile:\t %s\t%s\t%d%n", two.name, two.status, two.age);
    System.out.printf("Person three Profile: %s\t%s\t%d%n", three.name, three.status, three.age);
  }
}

//Class constructor
class Person{
  //object fields
  String name;
  String status;
  int age;

  //constructor
  Person(String name, String status, int age){
    //overloading... if you use different names you can remove 'this'
    this.name = name;
    this.status = status;
    this.age = age;
  }
}