Java Common Unchecked Exceptions – Vidvaan

There are some common unchecked exceptions occur in day to day java programming. Here we are going to see scenarios when those unchecked exceptions may occur.

1) NullPointerException

When access methods or variables on a null reference then throws NullPointerException

Employee emp = null;
emp.name = "sekhar"; // Accessing variable on null reference causes NullPointerException
emp.getName(); // Accessing method on null reference causes NullPointerException

Employee emp = null;

emp.name = "sekhar"; // Accessing variable on null reference causes NullPointerException

emp.getName(); // Accessing method on null reference causes NullPointerException

2) ArithmeticException

When an integer “divide by zero” throws ArithmeticException.

int result = 1/0; // Arithmetic Exception

1	int result = 1/0; // Arithmetic Exception

3) NumberFormatException

When we try to convert string into a numeric value such as float or integer or long but the format of the input string is not appropriate or illegal.

int x = Integer.parseInt(null); // Throws NumberFormatException
int y = Integer.parseInt("100A"); // Throws NumberFormatException

1 2	int x = Integer.parseInt(null); // Throws NumberFormatException int y = Integer.parseInt("100A"); // Throws NumberFormatException

4) ArrayIndexOutOfBoundsException

When access illegal index of an array

int[] values = new int[] {1, 2, 3};
int valueFromNegativeIndex = values[-1]; // access at negative index
int valueFromGreaterIndex = values[4];   // access at greater index
int valueFromLengthIndex = values[3];    // access at index equal to size of the array

int[] values = new int[] {1, 2, 3};

int valueFromNegativeIndex = values[-1]; // access at negative index

int valueFromGreaterIndex = values[4]; // access at greater index

int valueFromLengthIndex = values[3]; // access at index equal to size of the array

5) StringIndexOutOfBoundsException

When access illegal index of String with it’s methods

String name = "SomaSekhar Reddy";
char charAtNegativeIndex = name.charAt(-1); // access at negative index
char charAtLengthIndex = name.charAt(18);   // access at index equal to size of the string
		
int intAtNegativeIndex = name.codePointBefore(-1); // access at negative index
int intAtLengthIndex = name.codePointBefore(18);   // access at index equal to size of the string

String name = "SomaSekhar Reddy";

char charAtNegativeIndex = name.charAt(-1); // access at negative index

char charAtLengthIndex = name.charAt(18); // access at index equal to size of the string

int intAtNegativeIndex = name.codePointBefore(-1); // access at negative index

int intAtLengthIndex = name.codePointBefore(18); // access at index equal to size of the string

6) IllegalArgumentException

When a method has been called by passing an illegal or inappropriate argument

Thread thread = new Thread();
thread.sleep(-1);
thread.setPriority(20);

Thread thread = new Thread();

thread.sleep(-1);

thread.setPriority(20);

7) IllegalStateException

When a method has been invoked either at illegal or inappropriate time

package com.vidvaan.corejava.exception18.common.unchecked.exceptions;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

//common unchecked exception example : IllegalStateException
public class IllegalStateExceptionDemo {
	public static void main(String args[]) {
		List<String> arrayList = new ArrayList<String>();
		arrayList.add("a");
		arrayList.add("b");

		Iterator<String> it = arrayList.iterator();
		while (it.hasNext()) {
			it.remove();// calling remove() without calling next() throws IllegalStateException
		}
	}
}

package com.vidvaan.corejava.exception18.common.unchecked.exceptions;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

//common unchecked exception example : IllegalStateException

public class IllegalStateExceptionDemo {

public static void main(String args[]) {

List<String> arrayList = new ArrayList<String>();

arrayList.add("a");

arrayList.add("b");

Iterator<String> it = arrayList.iterator();

while (it.hasNext()) {

it.remove();// calling remove() without calling next() throws IllegalStateException

}

8) ClassCastException

Thrown to indicate that the code has attempted to cast an object to a subclass of which it is not an instance.

package com.vidvaan.corejava.exception18.common.unchecked.exceptions;

//common unchecked exception example : ClassCastException

class A {
}

class B extends A {
}

class C extends B {
}

public class ClassCastExceptionDemo {
	public static void main(String[] args) {
		A a = new B(); // B type is auto up casted to A type
		C c = (C) a; // Here, you will get class cast exception
	}
}

package com.vidvaan.corejava.exception18.common.unchecked.exceptions;

//common unchecked exception example : ClassCastException

class A {

}

class B extends A {

}

class C extends B {

}

public class ClassCastExceptionDemo {

public static void main(String[] args) {

A a = new B(); // B type is auto up casted to A type

C c = (C) a; // Here, you will get class cast exception

}