Sometime back I wrote an article on Top 50 Java Programming Questions. Our readers liked it a lot. So today we will look into some tricky interview questions in Java.
Java Tricky Interview Questions
These are programming questions but unless you have a deep understanding of Java, it will be hard to guess the output and explain it.
1. Null as Argument
We have overloaded functions and we are passing null. Which function will be called and what will be the output of the program?
public class Test {
public static void main(String[] args) {
foo(null);
}
public static void foo(Object o) {
System.out.println("Object argument");
}
public static void foo(String s) {
System.out.println("String argument");
}
}
2. Use “L” for long
Can you guess the output of the below statements?
long longWithL = 1000*60*60*24*365L;
long longWithoutL = 1000*60*60*24*365;
System.out.println(longWithL);
System.out.println(longWithoutL);
Explanation of Null Argument Tricky Question
According to Java specs, in case of overloading, the compiler picks the most specific function. Obviously String class is more specific than Object class, hence it will print “String argument”. But, what if we have another method in the class like below.
public static void foo(StringBuffer i){
System.out.println("StringBuffer impl");
}
In this case, the Java compiler will throw an error as “The method foo(String) is ambiguous for the type Test”. String and StringBuffer have no inheritance hierarchy. So none of them are more specific to others. A method is more specific than another if any invocation handled by the first method could be passed on to the other one without a compile-time type error. We can pass String as a parameter to Object argument and String argument but not to the StringBuffer argument method.
Explanation for Long Variable
The output of the code snippet will be:
31536000000
1471228928
We are explicitly creating the first variable as long by adding an “L” suffix. So the compiler will treat it as long and assign it to the first variable. For the second statement, the compiler will perform the calculation and treat it as a 32-bit integer. Since the output is outside the range of integer max value (2147483647), the compiler will truncate the most significant bits and then assign it to the variable. Binary equivalent of 1000*60*60*24*365L = 011101010111101100010010110000000000 (36 bits). After removing 4 most significant bits to accommodate in 32-bit int, the new value = 01010111101100010010110000000000 (32 bits). This is equal to 1471228928 and hence the output. Recently I have created a YouTube video series for java tricky programs.
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Great share. Thanks a lot! My score: 1/2. I could not answer Long prob right.
- Rishi Raj
Nice explaination :)
- Manjunath
Crystal Clear Explanation! but in the second case you converted the value to boolean, how can we achieve it in a min, any shortcuts?
- Shiva
Answer to question 1 is wrong. Kindly correct. public class NullArgumentTest { public static void main(String[] args) { method(null); } public static void method(Object o){ System.out.println(“Object imple”+o); System.out.println(“test”); } public static void method(String s){ System.out.println(“object impl”+ s); } } /*****Output*******/ object implnull So, Kindly reply.
- Karam
What’s wrong there, your output is same as mine.
- Pankaj
Your method is wrong as you are printing Object impl in case of string also. public static void method(String s){ System.out.println(“object impl”+ s); }
- Robin
lol :P that guy a noob :P
- Anshul
hi is printing (“object impl”+ s) and (“object imple”+ s) in case of object he is printing 2 statements
- Ankit
In my interview with Chetu India, there was one simple question which made me think twice:
public class HelloWorld { public static void main(String args[]){ boolean a = false; if(a=true){ System.out.println("a is true"); }else{ System.out.println("a is false"); } } }So, i hope this would help someone.- Karam
you can’t assign a null object to boolean first of all. You used if(a=null) supposed to be if(a==null)
- Nagendra Varma Mudunuri
It will print “a is true” because while jvm comes to if condition it will return true value so when if condition is true go to inside if block and print.
- Ajit sharma
if(a=true) is wrong statement ,so it will give error , if(a==true) should be there…
- Narayan Choudhary
if(a=true) ==>> a = true; if(a) So a is true will be printed
- Ponsuyambu
Thats no a “wrong statement”. true gets assigned, and the if block will get executed!!
- Sudhansu
it will not through any error it will simply run and print true.
- Avani
good
- abc
a=true a assign value =true in variable a answer is a is true
- farman
2 problem, compile time error…if(a==true), but u made it only =
- suresh
public class HelloWorld { public static void main(String args[]){ boolean a = false; if(a=true){ System.out.println(“a is true”); }else{ System.out.println(“a is false”); } } } No one can prove this is an incorrect question. In the if part you are first assigning a is to true & then the if condition will be examined & it is found true.
- Harsh Rasogi
ye the output of this program is true public class conditionalstate { public static void main(String args[]) { boolean a = false; //without any change if(a=true) { System.out.println(“a is true”); } else { System.out.println(“a is false”); } } } o/p a is true
- Suraj Vishwakarma
“a=true” is an assignment operation and not a relational operator. “a=true”, would return the value as true. Hence, you are getting a is true.
- Bishnu
public static void main(String[] args) { method(null); } public static void method(Object o) { System.out.println(“Object impl”); } public static void method(int s) { System.out.println(“Integer impl”); } public static void method(String s) { System.out.println(“String impl”); } could you explain to my Why the System print “String impl”. I couldn’t no understand it. I am sorry ab this silly question. bcoz im noob on java. Many thank.
- Logan
The method with String argument is taking precedence over the method with int argument is because of the primitive nature of int. If you decalre a method with the wrapper class pointed, then it will show you the same error with ambiguity.
- Sabeer Abdul Khadir Kutty
This is not about taking the precedence by String over int. It is clearly stated that there are three methods - with Object argument, with String argument and with int argument… and the value that is passed from main method is null which is of type ‘Object’. Since the type is Object, the overloaded method with int argument automatically disqualifies and the contest is now in between method with Object argument and String argument. Now, since the String is the more specific that the available Object argument/parameter, it qualifies for the execution. Thanks!
- Yubraj Subedi
you should put value in method(null); method(0); method(" "); i think u clearly know about opp’s Rule
- krishna
public class Test { public static void main(String args[]) { nullCheck(null); } public static void nullCheck(String s) { System.out.println(“string”); } public static void nullCheck(Object s) { System.out.println(“object”); } } //output String can anyone explain to me why out is String?
- Rajesh pawar
String is “More specifc” than object.Please read the above blog, this scenario is very beautifully explained.
- om
string is more specific than object that’s y it will be print the ‘string’
- reddy
in method overloading first preference is given to the child class. as String is child class of object and they are related(parent -->child) hence method with string parameter will be executed.
- Ankita
Null is valid for both string and object. But string is the child class of object. So if the work is being completed at child level then it is not required to for parent level… that’s why here string will dominant on object.
- Rakesh
I think your explanation of question 2 is not complete, you don’t make it clear that the L modifies only the constant 365… The multiplications are executed left to right, so in the first line of the example 1000*60*60*24 is computed in 32-bit arithmetic (it fits). The last operation multiplies that result by a long (365L) which forces the promotion to 64 bit. Observe: jshell> 1000*60*60*24 $4 ==> 86400000 jshell> 1000*60*60*24*365L $5 ==> 31536000000 jshell> 1000*60*60*24*365*1L $6 ==> 1471228928 jshell> 1000*60*60*24*365 $7 ==> 1471228928
- Chuck