Essential Java Collections and Exception Handling Tutorial

1. ArrayList Class – add, get, set, remove, size

import java.util.ArrayList;

ArrayList<String> list = new ArrayList<>();
list.add("A");                  // add
list.add("B"); 
String item = list.get(1);      // get
list.set(0, "C");               // set
list.remove("B");               // remove by value
int sz = list.size();           // size

2. Looping through an ArrayList

// Index-based loop
for(int i=0; i<list.size(); i++) {
    System.out.println(list.get(i));
}

// Enhanced for
for(String s : list) {
    System.out.println(s);
}

// Using Iterator
import java.util.Iterator;
Iterator<String> it = list.iterator();
while(it.hasNext()) {
    System.out.println(it.next());
}

3. Sorting an ArrayList

import java.util.Collections;
Collections.sort(list); // Sorts in natural order

4. LinkedList

import java.util.LinkedList;

LinkedList<String> llist = new LinkedList<>();
llist.add("Dog");
llist.addFirst("Cat");
llist.addLast("Parrot");
llist.remove("Cat");
System.out.println(llist);

5. HashMap – Key, Value Pair

import java.util.HashMap;

HashMap<String, Integer> map = new HashMap<>();
map.put("John", 24);
map.put("Jane", 32);
int age = map.get("John");
map.remove("Jane");

6. HashSet – add, remove, contains

import java.util.HashSet;

HashSet<String> set = new HashSet<>();
set.add("Red");
set.add("Blue");
set.remove("Red");
boolean hasBlue = set.contains("Blue");

7. Iterator

Iterator<String> iter = set.iterator();
while(iter.hasNext()) {
    System.out.println(iter.next());
}

8. Map.EntrySet – Iterating a HashMap

for(java.util.Map.Entry<String, Integer> entry : map.entrySet()) {
    System.out.println(entry.getKey() + ": " + entry.getValue());
}

9. Java Exception Handling

try {
    int result = 10 / 0;
} catch(ArithmeticException e) {
    System.out.println("Error: " + e.getMessage());
} finally {
    System.out.println("Cleanup code always runs!");
}

10. throw and throws Keywords

public void checkAge(int age) throws Exception {
    if(age < 18) {
        throw new Exception("Underage not allowed");
    }
}