How to create variables dynamically in Java?

Question

I need to create new variables Strings such that

String person1 = "female";
String person2 = "female";
........
........
String person60 = "male";
........
String person100 = "male";

This is what I tried

for (int i = 1; i <101; i++) {
  if (i<60) {
    String person+i = "female";
  }
  else {
    String person+i = "male";   
  }
}

Can anybody help me correct this code?

If I had a dollar for every time this type of question were asked here, I'd be a rich man. As an aside, I'd either use a boolean, male, or an enum `Sex {MALE, FEMALE}` — Hovercraft Full Of Eels, Oct 12 '13 at 15:58
@HovercraftFullOfEels If you find a question that's close enough to this one, flag (or close vote) this as a duplicate. — luiscubal, Oct 12 '13 at 19:25
OK @luiscubal: here's one of many duplicates: [dynamic variable names](http://stackoverflow.com/questions/2665655/create-variable-names-using-a-loop-in-java). Voting to close question as a duplicate. — Hovercraft Full Of Eels, Oct 12 '13 at 19:37

score 24 · Accepted Answer · answered Oct 12 '13 at 15:59

A Map allows you to relate any key with any value. In this case, the key is the name of the variable, and the value is the value

Map<String, String> details = new HashMap<>();
for (int i = 1; i <101; i++) {
    if (i<60) {
        details.put("person" + i, "female");
    }
    else {
        details.put("person" + i, "male");
    }
}

score 9 · Answer 2 · answered Oct 12 '13 at 15:57

You are close. If you store the the gender of each person in an array, you can do it like this:

String[] persons = new String[100]
for (int i = 0; i < persons.length; i++) {
  if (i<60) {
    persons[i] = "female";
  }
  else {
    persons[i] = "male";   
  }
}

Alternately, if a person is more than a gender, consider making a class Person that holds a gender field, and then have an array of Persons. You would set the gender in a similar way.

score 6 · Answer 3 · answered Oct 12 '13 at 15:58

6

You might use a Map<String,String> where the key is your "variable name" and the value is the value of that variable.

answered Oct 12 '13 at 15:58

Christian Fries

16,175
10
56
67

score 4 · Answer 4 · answered Oct 12 '13 at 15:57

You will need a String[] of some size that you can determine dynamically.
Then, assign values to the array elements.

String[] anArray;

// some magic logic

anArray = new String[100];
for(int i = 0; i < anArray.length; i++){
 // more magic logic to initialize the elements
}

Another option is a Vector<> or ArrayList<> like so:

List<String> anExpandableArray = new ArrayList<String>();
// add String data
anExpandaleArray.add("Foo");
anExpandaleArray.add("Bar");

T.J. Crowder · Answer 5 · 2013-10-12T16:05:28.777

When you find yourself wanting to create "more variables" of the same type, you usually want a list of some kind. There are two fundamental kinds of "lists" in Java: Arrays, and Lists.

An array:

String[] people = new String[10];               // That gives you room for 10

people[0] = "female";
people[1] = "male";
// ...
int n = 1;
System.out.println("Person " + n + " is " + people[n]);

A List:

List<String> people = new LinkedList<String>(); // Expandable
people.add("female");
people.add("male");
// ...
int n = 1;
System.out.println("Person " + n + " is " + people.get(n));
// Note difference -------------------------------^^^^^^^

Using an array is great when you know in advance how many there will be. Using a list is great when you don't know how many there will be.

Note on lists: There's an interface, List, and then there are multiple different concrete implementations of it with different runtime performance characteristics (LinkedList, ArrayList, and so on). These are in java.util.

score 3 · Answer 6 · answered Oct 12 '13 at 15:57

3

Just Use an array like so

String[] people = new String[numofelements];

And to initialise the array

for(int i = 0; i < people.length; i++){
      people[i] = "whatever";
}

answered Oct 12 '13 at 15:57

06needhamt

1,555
2
19
38

score 3 · Answer 7 · answered Oct 12 '13 at 15:58

3

String[] persons = new String[101];

for (int i = 0; i < 101; i++) {
    if (i < 60) {
       String persons[i] = "female";
    } else {
       String persons[i] = "male";   
    }
}

answered Oct 12 '13 at 15:58

user278064

9,982
1
33
46

How to create variables dynamically in Java?

7 Answers7

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