Random Class

1. Introduction

The Random class in Java (from java.util) is used to generate pseudo-random numbers.

It helps you generate values like:

• random integers
• random doubles
• random booleans
• random numbers within a range

The randomness is called pseudo-random because the values are generated using a mathematical algorithm based on a seed.
So the values look random, but they are actually predictable if the seed is known.

2. Why Random Class Is Needed

Although Math.random() exists, Random is preferred when you need:

• more methods (int, long, boolean, etc.)
• controlled range generation
• reproducible output using seed
• cleaner design for multiple random values

Random is widely used in:

• games
• simulations
• OTP-like demo systems
• randomized testing
• shuffling logic

3. Creating a Random Object

Basic creation:

import java.util.Random;

Random random = new Random();

This uses a default seed based on the current time.

If you want reproducible output:

Random random = new Random(100);

Using the same seed produces the same sequence.

4. Generating Random Integers

4.1 nextInt()

Random r = new Random();
int n = r.nextInt();
System.out.println(n);

This can be any integer value.

4.2 nextInt(bound)

Generates a number from 0 to bound - 1.

int n = r.nextInt(10);
System.out.println(n); // 0 to 9

5. Generating Random Numbers in a Range

If you need random number between min and max inclusive:

Example: 50 to 100

int min = 50;
int max = 100;

int n = r.nextInt((max - min) + 1) + min;
System.out.println(n); // 50 to 100

This is one of the most important patterns.

6. Random Double and Float

6.1 nextDouble()

Returns a double in the range:

• 0.0 (inclusive) to 1.0 (exclusive)

double d = r.nextDouble();
System.out.println(d);

6.2 nextFloat()

float f = r.nextFloat();
System.out.println(f);

7. Random Boolean

Returns true or false.

boolean b = r.nextBoolean();
System.out.println(b);

Used in simulations and random decisions.

8. Random Long and Other Types

long l = r.nextLong();
System.out.println(l);

Similarly:

• nextGaussian() gives values in a normal distribution (advanced use).

9. Seed Concept (Very Important)

A seed is the initial value used by the random generator.

If seed is fixed:

• output becomes predictable
• sequence becomes repeatable

Example:

Random r1 = new Random(10);
Random r2 = new Random(10);

System.out.println(r1.nextInt(100));
System.out.println(r2.nextInt(100));

Both lines print the same result.

This is useful for:

• testing
• debugging
• simulations where repeatability matters

10. Random vs Math.random()

Use Random when you need more flexibility.

11. Summary

• Random belongs to java.util.
• It generates pseudo-random values using a seed.
• Common methods: nextInt(), nextInt(bound), nextDouble(), nextBoolean().
• Range generation uses the formula: nextInt((max-min)+1)+min.
• Same seed produces same output sequence, useful for testing.
• Random is more flexible than Math.random().

Written By: Shiva Srivastava