I have a linked list with object person.
Class person{
int age;
String name;
String address
}
Now, I want to check if object is contained in the list. But my problem, is that only some fields are relevant. For example, I want to check if the person: tony, age 18 is contained in the list.
Are list support it? If not, which data structure support it?
Well, you could use a simple loop.
for (int i=0; i<list.size(); i++) {
Person p = list.get(i);
if (p.name.equals("Tony") && p.age == 18) {
//p is the person you were looking for
//do whatever you wanted to do with p
//if you don't want to include duplicate "Tonies" then add a break;
}
}
Well, you can put your persons in a List<Person> and iterate over it:
for(Person p : personList){
if ("tony".equals(p.name) && p.age == 18){
//match - do some stuff
;
}
}
List has method contains(obj) it compares (o==null ? e==null : o.equals(e))
So if you override equals method in your Person class, and you could do list.contains(obj) it returns you true/false directly.
This class can be mapped to a table at databse and you want to execute a select * from person where age > 18.
There are 2 cases to do it: on is without index: the databse will read all values and it will do a compare to age field value, the same is with list: parse the list elements and you will find for sure, but this is the slowest method.
Other one is an optimisation for search: add an index to database to relevant fields. In list you can have other data collection to speed up searching.
For example: LinkedHashSet> indexedByAge just ask it who is 18 or before 18 an you will get a series of ArrayList which need to merge to one with addAll() method.
You can check like this
ArrayList<Person> persons=new ArrayList<Person>();
To check persons
do like this
for(Person p : persons)
{
if (p.name.equals("Tony") && p.age == 18)
}
A bit messy, but you could override the equals method as follows:
class Person
{
int age;
String name;
String address;
Person(int a, String n, String ad) { age = a; name = n; address = ad; };
@Override
public boolean equals(Object o)
{
Person p = (Person)o;
if (p.age != -1 && age != -1 && p.age != age)
return false;
if (p.name != null && name != null && !p.name.equals(name))
return false;
if (p.address != null && address != null && !p.address.equals(address))
return false;
return true;
}
}
I'm assuming -1 and null are uninitialized values.
Usage:
ArrayList<Person> arr = new ArrayList<Person>();
arr.add(new Person(18,"tony","here"));
System.out.println(arr.contains(new Person(18,"tony",null))); // prints true
