>Digital-flame

OutputStream is an abstract class in java.io that represents an output stream of bytes — i.e., it lets you write raw binary data to some destination.

The class you’re looking for is DataInputStream.

SequenceInputStream in Java is a class used to combine two or more input streams into one so they can be read sequentially, one after the other, as if they were a single continuous stream.

    public static List<List<Integer>> permute(int[] nums) {
        List<List<Integer>> res = new ArrayList<>();
        dfsBacktrackingAllSubsets(nums, 0, new ArrayList<>(), res);
        return res;
    }

    private static void dfsBacktrackingAllSubsets(int[] nums, int index, List<Integer> prevCombination, List<List<Integer>> allCombinations) {
        List<Integer> newCombination = new ArrayList<>(prevCombination);
        newCombination.add(nums[index]);
        allCombinations.add(newCombination);

        if (index == nums.length - 1) {
            return;
        }

        dfsBacktrackingAllSubsets(nums, index + 1, prevCombination, allCombinations);
        dfsBacktrackingAllSubsets(nums, index + 1, newCombination, allCombinations);
    }

    public static List<List<Integer>> permute(int[] nums) {
        List<List<Integer>> res = new ArrayList<>();
        dfsBacktrackingAllPermutations(nums, 0, res);
        return res;
    }

    private static void dfsBacktrackingAllPermutations(int[] nums, int start, List<List<Integer>> result) {
        if (start == nums.length) {
            List<Integer> permutation = new ArrayList<>();
            for (int num : nums) {
                permutation.add(num);
            }
            result.add(permutation);
            return;
        }

        for (int i = start; i < nums.length; i++) {
            swap(nums, start, i); // choose
            dfsBacktrackingAllPermutations(nums, start + 1, result); // explore
            swap(nums, start, i); // un-choose (backtrack)
        }
    }

    private static void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }

✅ What Is PushbackInputStream?

PushbackInputStream is a special kind of InputStream that allows you to “unread” or push back bytes into the stream — so they can be read again later.

It’s like a stream with an “undo” buffer — ideal for building parsers or tokenizers.

Great question, Stanley! 🧠 Let’s explore the subclasses of InputStream and understand what each is used for.

InputStream is the abstract base class for reading raw bytes in Java.

✅ 1. java.io — Traditional I/O (Streams API)

This is the main package that contains most of the classic input/output stream classes.

✅ Main Classes of Input/Output Streams

🔹 1. Byte Streams

Use these for binary data (files, images, audio, etc.)

📥 Input Streams (read bytes):

• InputStream (abstract base class)
• FileInputStream – reads bytes from a file
• BufferedInputStream – adds buffering
• ByteArrayInputStream – reads from a byte array
• DataInputStream – reads primitive types (int, double, etc.)
• ObjectInputStream – reads serialized Java objects
• PipedInputStream – used for inter-thread communication

📤 Output Streams (write bytes):

• OutputStream (abstract base class)
• FileOutputStream – writes bytes to a file
• BufferedOutputStream – adds buffering
• ByteArrayOutputStream – writes to a byte array
• DataOutputStream – writes primitives
• ObjectOutputStream – writes serialized objects
• PipedOutputStream – connects to PipedInputStream

🔹 2. Character Streams

Use these for text (Unicode characters)

📥 Readers (read characters):

• Reader (abstract base class)
• FileReader – reads from a file
• BufferedReader – efficient line-by-line reading
• CharArrayReader – reads from a char array
• StringReader – reads from a string
• InputStreamReader – bridges byte → character stream

📤 Writers (write characters):

• Writer (abstract base class)
• FileWriter – writes to a file
• BufferedWriter – buffered writing
• CharArrayWriter – writes to char array
• StringWriter – writes to string
• OutputStreamWriter – bridges character → byte stream

🧠 Summary Table

🧠 Let’s walk through the types of input and output streams in Java — these are part of the traditional java.io package.

Java organizes streams into two main categories: