Java.Streams.What subclasses of the InputStream class do you know, what are they for?

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.

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✅ Common Subclasses of InputStream

Subclass	Purpose
FileInputStream	Reads bytes from a file
ByteArrayInputStream	Reads bytes from a byte array in memory
BufferedInputStream	Adds a buffer to another input stream for better performance
DataInputStream	Reads primitive types (int, double, etc.) in a portable way
ObjectInputStream	Deserializes Java objects previously written with ObjectOutputStream
PipedInputStream	Used for inter-thread communication (connected to PipedOutputStream)
SequenceInputStream	Combines multiple streams into one continuous stream
FilterInputStream	Abstract decorator for filtering input (base for other filters)
PushbackInputStream	Allows pushing bytes back into the stream (for parsers)

🔍 Explanation with Use Cases

🔹 FileInputStream

Reads raw bytes from a file (e.g. reading an image or binary data).

InputStream in = new FileInputStream("data.bin");

🔹 ByteArrayInputStream

Simulates an input stream from a byte array — no actual file or network involved.

byte[] data = {1, 2, 3};
InputStream in = new ByteArrayInputStream(data);

🔹 DataInputStream

Reads Java primitive data types like int, double, boolean in a portable way.

DataInputStream in = new DataInputStream(new FileInputStream("data.bin"));
int age = in.readInt();

🔹 ObjectInputStream

Reads (deserializes) objects written with ObjectOutputStream.

ObjectInputStream in = new ObjectInputStream(new FileInputStream("object.dat"));
MyClass obj = (MyClass) in.readObject();

🔹 PipedInputStream

Used for communication between threads.

PipedInputStream in = new PipedInputStream();
PipedOutputStream out = new PipedOutputStream(in);

🔹 SequenceInputStream

Concatenates multiple input streams into one.

SequenceInputStream in = new SequenceInputStream(in1, in2);

🔹 PushbackInputStream

Supports unreading (pushing back) bytes into the stream — useful for custom parsers.

PushbackInputStream in = new PushbackInputStream(new FileInputStream("input.txt"));

🧠 Summary Table

Subclass	Reads From	Special Feature
FileInputStream	File	Raw binary file access
ByteArrayInputStream	Byte array	In-memory data stream
BufferedInputStream	Any stream	Adds buffering
DataInputStream	Any stream	Reads Java primitives
ObjectInputStream	Any stream	Reads objects (serialization)
PipedInputStream	Another thread	Inter-thread pipe input
SequenceInputStream	Multiple streams	Concatenates input
PushbackInputStream	Any stream	Allows “unread” of bytes