In this example we will discuss how to remove objects from a java.util.List.
There are 2 methods described in the Java API to do so :
- E remove(int index)
We can use index of list to remove the object.
- boolean remove(Object o)
We can pass the object itself which needs to be removed. For this method to work for objects we have to make sure that the equals() method is properly overridden.
Lets see both of them in examples.
1) remove(int index)
// making a list of string objects
List strList = new ArrayList();
strList.add("one");
strList.add("two");
strList.add("three");
for (String string : strList) {
System.out.println(string);
}
strList.remove(1);
System.out.println("**** After Removal by Index ****");
for (String string : strList) {
System.out.println(string);
}
// making a list of user objects
List userList = new ArrayList();
userList.add(new User("abcd", "pqrs"));
userList.add(new User("abcd1", "pqrs1"));
userList.add(new User("abcd2", "pqrs2"));
for (User user : userList) {
System.out.println(user);
}
//removing user by index
userList.remove(0);
System.out.println("**** After Removal by Index for User List ****");
for (User user : userList) {
System.out.println(user);
}
2) remove(Object o)
// remove String from string list
strList.remove("one");
System.out.println("**** After Removal by Object ****");
for (String string : strList) {
System.out.println(string);
}
//removing by user object
userList.remove(new User("abcd1","pqrs1"));
System.out.println("**** After Removal by User Object ****");
for (User user : userList) {
System.out.println(user);
}
The User Class
package com.javacodegeeks.example;
public class User {
private String firstName;
private String lastName;
public User(String firstName, String lastName) {
super();
this.firstName = firstName;
this.lastName = lastName;
}
//setters and getters
@Override
public String toString() {
return firstName + " " + lastName;
}
@Override
public boolean equals(Object obj) {
return (this.firstName.equals(((User) obj).firstName) && (this.lastName
.equals(((User) obj).lastName)));
}
}
In the above example, we passed the object which was to be removed from the ArrayList. The important point to note here is that we had to make sure that the equals method was overridden properly for the remove(object) method to work.
Download the Eclipse project of this tutorial
Download
You can download the full source code of this example here : JavaListRemoveObjectExample.zip
You can download the full source code of this example here : JavaListRemoveObjectExample.zip
