Interview Question And Answer in java

Q.1:   Is the code compiles ? If yes then what will be the output ?
Ans.
class IntegerValue { public static void main(String[] args) { Integer i1 = 128; Integer i2 = 128; System.out.println(i1 == i2); Integer i3 = 127; Integer i4 = 127; System.out.println(i3 == i4); } } Output :      false
                  true
Q.2: Is the code compiles ? If yes then what will be the output ?
Ans.
class a{ static{System.out.println("s1");} public String GetCityname(String s){ return "String"; } } class b extends a{ static{System.out.println("s2");} public String GetCityname(String s1){ return "StringBuffer"; } } public class LogicTest extends b{ static{System.out.println("s3");} public static void main(String[] args) { System.out.println("post"); LogicTest o=new LogicTest(); System.out.println(o.GetCityname("mano")); System.out.println("stop"); } } Output :      s1
                  s2
                  s3
                  post 
                 StringBuffer 
                 stop
Q.3: Is the code compiles ? If yes then what will be the output ?
Ans.
class StaticDemo{ static { i=10; System.out.println("r10"); } static { i=11; System.exit(0); } static int i; public static void main(String[] args) { StaticDemo obj= new StaticDemo(); obj.i=20; System.out.println("i= "+StaticDemo.i); } }
Output :   r10
Q4. : Is the code compiles ? If yes then what will be the output ?
Ans.
class equal{ public void run(){ String s1="manoj"; String s2=new String("manoj"); if(s1==s2){ System.out.println("run method output: S1==S2 is True"); }else if(s1.equals(s2)){ System.out.println("run method output: s1.equals(s2) is true"); } else{ System.out.println("run method output: Not equals"); } } public void run1(){ String s1="manoj"; s1.concat("kumar1434@gmail.com"); String s2="manoj"; if(s1==s2){ System.out.println("run1 method output: S1==S2 is True"); }else if(s1.equals(s2)){ System.out.println("run1 method output: s1.equals(s2) is true"); } else{ System.out.println("run1 method output: Not equals"); } } } public class StringEqualAppend { public static void main(String[] args) { equal resul=new equal(); resul.run(); resul.run1(); } }
Output:          run method output: s1.equals(s2) is true
                     run1 method output: S1==S2 is True
Q.5:Is the code compiles ? If yes then what will be the output ?
Ans.
class logiTest { public static void main(String[] args) { int i=1; if(i++>1) System.out.println(i--); else System.out.println(i++); } }
Output :   2
Q.6:Is the code compiles ? If yes then what will be the output ?
Ans.
class nullPoint { public static void main(String[] args) { Integer i=null; int j=i; System.out.println(j); } }
Output :          java.lang.NullPointerException.
Q. 7: Is the code compiles ? If yes then what will be the output ?
Ans.
class test1 { public static void main(String[] args) { String s3 = "Hello Manoj"; int start = 4; char end = 11; System.out.println(start + end); System.out.println(s3.substring(start, end)); } }
Output:         15
                    o Manoj
Q.8: Is the code compiles ? If yes then what will be the output ?
Ans.
class A{ static int a = 9999; static { a = a-- - --a; System.out.println("Run1---: "+a); } static { a = a++ + ++a; System.out.println("Run2+++: "+a); } public static void main(String[] args) { System.out.println("Run Main Body : "+a); } }
Output :     Run1---: 2
                 Run2+++: 6
                 Run Main Body : 6
Q.9: Is the code compiles ? If yes then what will be the output ?
Ans.
class testDemo { public int number(int n) { System.out.println("public int"); return n; } protected Integer number(Integer n) { System.out.println("protected int"); return n; } protected Object number(Object n){ System.out.println("object"); return n;} private String number(String d) { System.out.println("String"); return "n"; } public static void main(String[] args) { testDemo n12 = new testDemo(); n12.number(10); n12.number(785.68); n12.number("manojkumar"); int a[]={10,20,30,05}; int b; b=a.length; System.out.println(b); } }
Output :             public int
                         object
                         String
                         4