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Collections Beginner

Stack to Deque and ArrayDeque

Use the Deque interface with ArrayDeque instead of the legacy Stack class.

Code Comparison

✕ Legacy Stack

Stack<String> stack = new Stack<>();
stack.push("task");
String next = stack.pop();

✓ Deque API

Deque<String> stack = new ArrayDeque<>();
stack.push("task");
String next = stack.pop();

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Why the modern way wins

🎯

Better abstraction

Deque explicitly models both stack and queue operations.

⚡

Lower overhead

ArrayDeque avoids Vector's legacy synchronization.

🧩

More flexible

The same interface supports LIFO and FIFO algorithms.

Old Approach

Stack

Modern Approach

Deque with ArrayDeque

Since JDK

Difficulty

Beginner

JDK Support

Stack to Deque and ArrayDeque

Available

Available since JDK 6 (December 2006)

How it works

Stack extends the legacy synchronized Vector class. Deque models stack operations directly, and ArrayDeque is the preferred general-purpose implementation for in-memory LIFO work.

Sequenced collections

Java 8

// Get last element
Object last = list.get(list.size() - 1);
// Get first
Object first = list.get(0);
// Reverse iteration: manual

Java 21+

var last = list.getLast();
var first = list.getFirst();
var reversed = list.reversed();

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JDK 21+ →

Collections Beginner

Reverse list iteration

Java 8

for (ListIterator<String> it =
        list.listIterator(list.size());
    it.hasPrevious(); ) {
    String element = it.previous();
    System.out.println(element);
}

Java 21+

for (String element : list.reversed()) {
    IO.println(element);
}

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JDK 21+ →

Collections Beginner

Immutable list creation

Java 8

List<String> list =
    Collections.unmodifiableList(
        new ArrayList<>(
            Arrays.asList("a", "b", "c")
        )
    );

Java 9+

List<String> list =
    List.of("a", "b", "c");

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JDK 9+ →