PrintStream is a subclass of FilterOutputStream that adds functionality for printing various data values in human-readable text format. It’s commonly used for printing output to the console, files, or any other output stream.
- Automatically converts primitives and objects to string representation.
- Methods like
print(),println(), andprintf()are provided. - You can control whether to auto-flush the stream after writing a newline or not.
- Does not throw IOException for each write, unlike other streams.
Commonly Used Constructors and Methods
Simple Program – Write to Console
Use PrintStream to display different types of data on the console in a formatted manner.
import java.io.*;
public class SimplePrintStreamDemo {
public static void main(String[] args) {
PrintStream ps = new PrintStream(System.out);
ps.println("Welcome to PrintStream Demo!");
ps.print("The value of PI is: ");
ps.println(Math.PI);
ps.printf("Formatted Output: %-10s | %-5d%n", "Mahesh", 90);
ps.close();
}
}
/*
Welcome to PrintStream Demo!
The value of PI is: 3.141592653589793
Formatted Output: Mahesh | 90
*/Problem Statement:
LotusJavaPrince and Mahesh are developing a banking system. They want to log transaction details to a file using PrintStream. Every time a transaction occurs, the system must write a readable message with user and amount.
import java.io.*;
class TransactionLogger {
private PrintStream logStream;
public TransactionLogger(String filename) throws FileNotFoundException {
logStream = new PrintStream(new FileOutputStream(filename, true));
}
public void logTransaction(String user, double amount) {
logStream.printf("User: %-15s | Amount: ₹%.2f%n", user, amount);
}
public void close() {
logStream.close();
}
}
public class BankTransactionApp {
public static void main(String[] args) {
try {
TransactionLogger logger = new TransactionLogger("transactions.txt");
logger.logTransaction("LotusJavaPrince", 1500.50);
logger.logTransaction("Mahesh", 2200.75);
logger.close();
System.out.println("Transactions logged successfully.");
} catch (FileNotFoundException e) {
System.err.println("Error opening log file.");
}
}
}Output
User: LotusJavaPrince | Amount: ₹1500.50
User: Mahesh | Amount: ₹2200.75Code language: HTTP (http)PrintStream simplifies printing of all types to streams.
- Supports formatted output similar to C’s
printf. - Ideal for logging and user-friendly outputs.
- Works seamlessly with files, sockets, and console.