Exception – Java2Blog

[Fixed] IllegalArgumentException: Bound must be positive

Java2blog — Sat, 17 Sep 2022 18:37:33 +0000

In this post, we will see how to fix IllegalArgumentException: Bound must be positive in java.

You will generally get this exception while generating random numbers using Random.nextInt() method. If you pass bound as 0 or less than 0, then you will get the exception.

Let’s understand with the help of example:

package org.arpit.java2blog;

import java.util.Random;

public class GenerateRandomNumberMain {

    public static void main(String[] args) {
        System.out.println("============================");
        System.out.println("Generating random number");
        System.out.println("============================");
        Random randomGenerator=new Random();
        System.out.println(randomGenerator.nextInt(0) + 1);
    }
}

When you run the code, you will get following exception.

============================
Generating random number
============================
Exception in thread "main" java.lang.IllegalArgumentException: bound must be positive
    at java.base/java.util.Random.nextInt(Random.java:388)
    at org.arpit.java2blog.GenerateRandomNumberMain.main(GenerateRandomNumberMain.java:12)

As we have passed bound as 0 to nextInt(), we got above exception.

Here is source code Random’s nextInt() method.

public int nextInt(int bound) {
        if (bound <= 0)
            throw new IllegalArgumentException(BadBound);

        int r = next(31);
        int m = bound - 1;
        if ((bound & m) == 0)  // i.e., bound is a power of 2
            r = (int)((bound * (long)r) >> 31);
        else {
            for (int u = r;
                 u - (r = u % bound) + m < 0;
                 u = next(31))
                ;
        }
        return r;
    }

As you can see, if bound is less than or equals to 0, we will get this exception.

To resolve the issue, pass positive number to nextInt() method.

Here is code to generate random number between 1 to 5.

package org.arpit.java2blog;

import java.util.Random;

public class GenerateRandomNumberMain {

    public static void main(String[] args) {
        System.out.println("============================");
        System.out.println("Generating random number");
        System.out.println("============================");
        Random randomGenerator=new Random();
        System.out.println(randomGenerator.nextInt(5)+1);
    }
}

When you run the code, you will get following exception.

============================
Generating random number
============================
2

As you can see, we have passed bound as 5 to nextInt() method and it worked fine now.

[Solved] Exception in thread “main” java.lang.NullPointerException

Java2blog — Tue, 06 Apr 2021 14:00:13 +0000

In this tutorial, we will see the most frequent java exception i.e. Exception in thread main java.lang.NullPointerException. It is one of the Runtime Exception.

Raise your hand if you ever got NullPointerException while working on java code. I am sure that this is the exception you might have encountered most frequently. You might also agree that NullPointerException is pain for most of java developers(novice or expert), but there is not much we can do about them, because this is the price we need to pay for convenient or unavoidable null references.

Reasons for NullPointerException

Reasons for NullPointerException as defined by Java docs.

Invoking the instance method of a null object.
Accessing or modifying the field of a null object.
Taking the length of null as if it were an array.
Accessing or modifying the slots of null as if it were an array.
Throwing null as if it were a Throwable value.
When you add null to Collections which do not allow nulls such as [ConcurrentHashMap](https://java2blog.com/concurrenthashmap-in-java/ “ConcurrentHashMap”)
Trying to synchronize using null object.

Let’s understand each of these in detail. I am creating a Employee class which we are going to use in our examples.

package org.arpit.java2blog;

public class Employee {
    String name;
    int age;

    public Employee()
    {

    }

    public Employee(String name, int age) {
        this.name=name;
        this.age=age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }

}