System.out.println() and System.out.print() in Java: Detailed Explanation

Console output is a fundamental part of Java programming, and System.out.println() and System.out.print() are essential tools for this purpose. Let’s break down what they are, how they work, and what the differences are.

1. What Are System.out.println() and System.out.print()?

In Java, the object System.out is used to display data on the screen. This object is the standard output stream, and by default, it prints text to the console. It has two main methods:

• System.out.print() – prints text to the console without moving to a new line.
• System.out.println() – prints text to the console and moves the cursor to a new line after printing.

Example of using print()

public class PrintExample {
    public static void main(String[] args) {
        System.out.print("Hello");
        System.out.print(" world!");
    }
}

Console output:

Hello world!

Both strings are printed on the same line since print() doesn’t move the cursor to a new line.

Example of using println()

public class PrintlnExample {
    public static void main(String[] args) {
        System.out.println("Hello");
        System.out.println("world!");
    }
}

Console output:

Hello
world!

println() automatically moves the cursor to the next line after printing.

2. When Does a Line Break Occur?

A new line is created in Java when:

1. Using System.out.println(), as this method adds a \n character at the end of the output.
2. Manually adding \n inside print(), for example: System.out.print("Hello\n"); System.out.print("world!\n"); Output: Hello world! This code works similarly to println().

3. Understanding System.out.println(): What Is What?

Breaking down System.out.println("Hello");:

• System – a predefined class from the java.lang package.
• out – a static field of the System class, representing an instance of the PrintStream class.
• println() – a method of the PrintStream class that prints text to the console.

Detailed Breakdown

a) System – The Class

System is a predefined class from the java.lang package. It provides access to standard input, output, and error streams, along with other utility methods, such as:

• System.out – the standard output stream.
• System.in – the standard input stream (usually the keyboard).
• System.err – the standard error stream.
• System.exit(0) – terminates the program.

Why don’t we need to import System?
The System class is in java.lang, which is automatically included in every Java program.

b) out – The PrintStream Object

Inside System, there is a static field out, which is an instance of the PrintStream class.

In Java’s source code, you can find:

public static final PrintStream out;

This means:

• The field out is static (static), so we call it as System.out without creating a System object.
• The field is final, meaning it cannot be reassigned.
• PrintStream is a special class that handles printing data to the console.

c) println() – Method of the PrintStream Class

The println() method performs two tasks:

1. Prints the provided text to the console.
2. Adds a new line (\n) at the end.

In the PrintStream class, println() is implemented like this:

public void println(String x) {
    synchronized (this) {
        print(x);
        newLine();
    }
}

• print(x); – prints the text without a new line.
• newLine(); – moves the cursor to a new line.

4. Common Errors and Nuances

1. Missing Space with print() System.out.print("Hello"); System.out.print("world!"); Output: Helloworld! (words are merged).
   Corrected version: System.out.print("Hello "); System.out.print("world!");
2. Unexpected Output When Concatenating Strings and Numbers System.out.println("5 + 3 = " + 5 + 3); Output: 5 + 3 = 53 (because "5 + 3 = " is a string, so 5 + 3 are converted into strings).
   Correct version: System.out.println("5 + 3 = " + (5 + 3)); Output: 5 + 3 = 8.
3. String Literal Error System.out.println("Hello world!); ❌ Compilation error: “unclosed string literal” (missing closing quote ").
4. Printing an Empty Line System.out.println(); ✅ Allowed, simply moves the cursor to a new line.

5. When to Use print vs println?

6. Where Does the System.out Object Come From?

Here’s an approximate example of how the JVM sets up System.out:

PrintStream myOutput = new PrintStream(System.out);
System.out = myOutput; // (in reality, out is final)