Question

我是一名使用Java的初学者，但我找不到解决方案：

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我想在for中添加参数，例如public class Company{ private String name; private int age; public Company(String n, int a){ name = n; age = a; } /*get and set*/ public static void main(String[] args) { ArrayList<Company> comp = new ArrayList<Company>(); comp.add(new Company("Tom", 23)); comp.add(new Company("John", 43)); comp.add(new Company("Charles", 25)); } }，email等。但address适用于新元素，没有参数。

Answer 1

您需要阅读有关课程members的内容。

public class Company{
  private String name;
  private int age;
  private String email;
  private String address;

  public Company(String n, int a, String e, String addr){
    name = n;
    age = a;
    email = e;
    address = addr;
  }

Answer 2

使用Company，email字段（1）扩展address类，更新构造函数（2），并传递所需的参数（3）。

public class Company {
    ...
    private final String address; // 1
    private final String email;

    public Company(String n, int a, String address, String email) { // 2
        ...
        this.address = address;
        this.email = email;
    }

    public static void main(String[] args) {
        ...
        comp.add(new Company("Charles", 25, "street", "charles@gmail.com")); // 3
    }

}

如果您已经有一个填充了特定字段信息的数组，则可以使用for：

final List<String> emails = Arrays.asList("first@gmail.com", "second@gmail.com");
for (final String email : emails) {
    comp.add(new Company(..., ..., ..., email));
}

Answer 3

首先，您需要向类添加变量（即每个类实例存储的位置，以及目前的名称或年龄

您必须修改构造函数（或创建另一个）才能获取这些参数，并且最好让getter和setter单独获取或设置这些参数，因此它看起来像这样

public class Company{
  private String name;
  private int age;
  private String email;
  private String address;

  public Company(String n, int a){
    name = n;
    age = a;            
  }

 public Company(String n, int a,String email, String address){
    name = n;
    age = a;            
    this.email = email;             //class instance object email is set to email from method parameter
   this.address = address;
  }

  /*get and set*/
  public void setEmail(String email){
    this.email=email; //explicit setter
  }

  public String getEmail(){
    return this.email;
  }

  public static void main(String[] args) {
        ArrayList<Company> comp = new ArrayList<Company>();
        comp.add(new Company("Tom", 23));  //will work, because I let your constructor
        comp.add(new Company("John", 43));
        comp.add(new Company("Charles", 25));           

        Company compToAdd= new Company("preparedFoo",22);
        compToAdd.setEmail("fooomail"); //will work because setter
        comp.add(compToAdd);           


        comp.add(new Company("FooName", 30,"fooMail","FooAddress"));   //will work because new constructor

    }

}

添加新参数以使用Java ArrayList

3 个答案: