问题
Person.java
public class Person {
public String firstName, lastName;
public Person(String firstName,
String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}
public String getFullName() {
return(firstName + " " + lastName);
}
}
PersonTest.java
public class PersonTest {
public static void main(String[] args) {
Person[] people = new Person[20]; //this line .
for(int i=0; i<people.length; i++) {
people[i] =
new Person(NameUtils.randomFirstName(),
NameUtils.randomLastName()); //this line
}
for(Person person: people) {
System.out.println("Person's full name: " +
person.getFullName());
}
}
}
In above code, we used twice "new". Is this code is correct or wrong? First one is for allocation of array. But why the second one? It's from lecture notes.
回答1:
Yes, it is correct.
The line:
Person[] people = new Person[20]
allocates the array, full of references to null while the line:
new Person(NameUtils.randomFirstName(),
NameUtils.randomLastName()); //this line
fills it [the array] by instantiating objects of type Person, and assigning the reference in the array.
回答2:
new Person[20] creates an array that can hold 20 references to Person objects. It does not create any actual Person objects.
new Person(...) creates a Person object.
The critical distinction to make here is that unlike in C or C++, new Person[20] does not allocate memory for 20 Person objects. The array does not contain the actual objects; it only contains references to them.
回答3:
Person[] people = new Person[20];
only allocates memory for objects Person (filled with nulls). Then you need to fill it with particular Persons (with random name and surname int this example).
来源：https://stackoverflow.com/questions/10044394/allocating-for-array-and-then-using-constructor