如何覆盖对象的ArrayList的ToString方法？

Question

class Person {
  public String firstname;
  public String lastname;
}

Person p1 = new Person("Jim","Green");
Person p2 = new Person("Tony","White");

ArrayList<Person> people = new ArrayList<Person>();

people.add(p1);
people.add(p2);

System.out.println(people.toString());

I'd like the output to be [Jim,Tony] , what is the simplest way to override the ToString method if such a method exists at all?

Answer 1

You actually need to override toString() in your Person class, which will return the firstname, because, ArrayList automatically invokes the toString of the enclosing types to print string representation of elements.

@Override
public String toString() {
    return this.firstname;
}

So, add the above method to your Person class, and probably you will get what you want.

PS : - On a side note, you don't need to do people.toString() . Just do System.out.println(people) , it will automatically invoke the toString() method for ArrayList .

Answer 2

You can write a static helper method on the Person class:

public static String toString(ArrayList<Person> people) {

    Iterator<Person> iter = people.iterator();

    ....


}

Answer 3

Write override method toString() method in Person class.

public String toString() {
    return firstname;
}

Answer 4

在这种情况下，您必须覆盖Person类的toString方法，因为arrayList只是迭代Person类实例。