Java Keywords
Java Keywords
* Keywords are predefined identifiers available directly
throughout the JVM.
* They have a special meaning inside java source code and
outside of comments and strings.
* For Example : public, static, void
Q1) What are different types of access modifiers in
Java?
Ans) There are four different types of modifiers:
| Modifier |
Accessible in the same package |
Accessible in different package |
| Private |
No |
Yes, only if the class extends the main class |
| Protected |
Yes |
Yes, only if the class extends the main class |
| Default |
Yes |
No |
| Public |
Yes |
Yes |
Q2) What is the use of final keyword?
Ans) The final keyword can be assigned to
- Class level variable
- method
- class
- Objects
If a final is assigned to a variable, the variable behaves as a
constant. It means that the value of variable once set cannot be
changed.
final int i=1;
i =5; // error
If a final is assigned to a method then it cannot be overridden
in its child class.
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package com.javasunderesan;
class Parent {
final void print() {
System.out.println("Inside");
}
}
class Child extends Parent {
public final void print() {// error cannot override final method
System.out.println("Inside");
}
}
|
If a class is made as final, then no other class can extend it
and make it as parent class. E.g. String Class.
Final objects are instantiated only once. i.e
final Map map
= new HashMap();
map.put("key","value");
map = new
HashMap(); // error
Q3) What is use of throws keyword?
Ans) The Java throws keyword is used to declare an exception. It
gives an information to the programmer that there may occur an
exception so it is better for the programmer to provide the exception
handling code so that normal flow can be maintained. Exception
Handling is mainly used to handle the checked exceptions. If there
occurs any unchecked exception such as NullPointerException, it is
programmers fault that he is not performing check up before the code
being used.
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package com.javasunderesan;
import java.io.IOException;
public class ThrowsKeyword {
void callTestThrow_1() throws IOException {
throw new IOException("device error");// checked exception
}
void callTestThrow() throws IOException {
callTestThrow_1();
}
void test() {
try {
callTestThrow();
} catch (Exception e) {
System.out.println("exception handled");
}
}
public static void main(String args[]) {
ThrowsKeyword obj = new ThrowsKeyword();
obj.test();
System.out.println("normal flow...");
}
}
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Output
exception handled
normal
flow...
Q4) Why static methods cannot access non static
variables or methods?
Ans) A static method cannot access non static variables or
methods because static methods doesn't need the object to be accessed.
So if a static method has non static variables or non static methods
which has instantiated variables they will no be initialized since the
object is not created and this could result in an error.
Q5) What is a static method?
Ans)A method defined as static is called static method. A static
method can be accessed without creating the objects. Just by using the
Class name the method can be accessed. Static method can only access
static variables and not local or global non-static variables. For eg:
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package com.javasunderesan;
public class StaticMethodExample {
public static void main(String args[]) {
MainClass.printMe();
}
}
class MainClass {
public static void printMe() {
System.out.println("Welcome to JavaSunderesan.blogspot.in");
}
}
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OutPut:
Hello World
Also static method can call only static methods and not non static
methods. But non-static methods can call static mehtods.
