Lists Interfaces - Java

Question

Again, this is based off the videos, documentation and notes that I made. I hope I'm not too far off because I think going back and writing these notes from the last view videos has been very useful. I don't quite get everything yet but that's a far cry from 2 weeks ago when this stuff in this course went completely over my head and I was bundling through.

Lists

The first interface in the collection is a List Interface. - http://docs.oracle.com/javase/8/docs/api/java/util/List.html
Lists are an ordered collection of items. In Java Lists, you can insert or replace items wherever you want to by index within a zero based index. You can check if something is in a list and sort it.
There are ArrayLists and LinkedLists.
ArrayList implements the list interface. You usually start with using ArrayLists.
To use Lists you need to implement something like List<String> this example is a "List of Strings"

List<String> fruit = new ArrayList<String>();

//using a method on an arrayList
fruit.isEmpty();

To use Lists you need to implement something like  List<String>  this example is a "List of Strings"

.add()
.remove()
.size()
.isEmpty()
.contains()
.add(1, "element to add here");


Collections.sort(fruit);  //interface must be Comparable

e.g.

List<String>  fruit  = new ArrayList<String>();
implementation           definition

To return an Object Array to a String Array()
fruit.toArray();
fruit.toArray(new String[0]);

asList()  pass in a String array and return it as a List.

Using ArrayLists

import java.util.ArrayList;
import java.util.List; import the List Interface.


//return a list of strings that start with #
public List<String> getHashTags() {
  //store a new list of strings using List.
  List<String> results = new ArrayList<String>();

 //loop through a set of words in a Treet getWords method
  for(String word : getWords()) {
     //dynamically add words to the list if they begin with a #
     if(word.startsWith("#")) {
        results.add(word);
     }
  }
  return results;
}

//code for getting mentions

public List<String> getMentions() {
  List<String> results = new ArrayList<String>();

  for(String word : getWords()) {
     //dynamically add words to the list if they begin with a @
     if(word.startsWith("@")) {
        results.add(word);
     }
  }
  return results;
}



instead use methods like this

public List<String> getHashTags() {
  return getWordsPrefixedWith("#");
}
public List<String> getMentions() {
  return getWordsPrefixedWith("@");
}


public List<String> getWordsPrefixedWith(String prefix) {
  List<String> results = new ArrayList<String>();

  for(String word : getWords()) {
     //dynamically add words to the list if they begin with a @
     if(word.startsWith(prefix)) {
        results.add(word);
     }
  }
  return results;
}

Object References

When we add objects to a collection, arrays included, we're actually adding the Object reference.
A reference is used to point to a specific place in memory.
When object values are changed they're kept because they're references to points in memory.

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Jonathan Grieve

Jonathan Grieve

Lists Interfaces - Java

Lists

Using ArrayLists

Object References

Nelson Fleig

Nelson Fleig

Jonathan Grieve

Jonathan Grieve