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why we write public static void main (String args[])
in core java plz explain briefly??????????????????
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Answer / nilay
because in JAVA everything is within class and should be
called with classname(static methods) or with instance of
that class. but main is the first method to be called when
no instances are in memory so that is why it is static and
is called like <classname>.main() by System class. and it
must be public because it is called from outside enviornent
of current class file. String[] is for the command line
arguments that you pass when you run your java program
by "java .classfile arg1 arg2" so all arguments are
received here and for multiple arguments it is an array of
strings. it does not return anything so it's return type is
void.
| Is This Answer Correct ? | 17 Yes | 0 No |
Answer / sreenivas p
JVM looks for the main method(from where it starts
execution) with the same signature(public static void
main(String args[])) if it coud not find throws
NoSuchMethodError.
valid signatures are:
public static void man(String args[])
static public void main(String a[])
Invalid signatures
static void main()
public static main(String args[]) etc..[treats these
are all as general methods ]
| Is This Answer Correct ? | 16 Yes | 3 No |
we write public because it can be called from outside the envornment and as we know that by using public keyword we will be able to access all the codes from outside,static is used because the JVM(java virtual machine which is also called as the interpreter calles the main function when there is no declaration of class instances so if we dont use static then the interprter will not check for it ,we use string and its a kind of class.It is also known as the commad line argument.
| Is This Answer Correct ? | 3 Yes | 0 No |
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Question 7 [8] Consider the following class and answer the questions below it: public class StackWithGuard extends Stack { public StackWithGuard(int size) { super(size); } synchronized public boolean isEmpty() { return super.isEmpty(); } synchronized public boolean isFull() { return super.isFull(); } synchronized public int getSize() { return super.getSize(); } synchronized public void push(Object obj) { try { while (isFull()) { wait(); } } catch (InterruptedException e) {} super.push(obj); COS2144/102 11 notify(); } synchronized public Object pop() { try { while (isEmpty()) { wait(); } } catch (InterruptedException e) {} Object result = super.pop(); notify(); return result; } public static void main(String args[]) { StackWithGuard stack = new StackWithGuard(5); new Producer(stack, 15).start(); new Consumer(stack, 15).start(); } } Note: The Stack class is provided in the Appendix. Note also: The following questions all refer to the pop() method of the StackWithGuard class given above. 7.1 What does the synchronized keyword ensure for this method? (2) 7.2 Why is a while loop used to test whether the stack is empty? In other words, why wouldn't the following if statement be sufficient? if (isEmpty()) { wait(); } (2) 7.3 Why is the result of popping (provided by the inherited pop() method) stored in a temporary variable? In other words, why wouldn't the following statement be sufficient? return super.pop(); (2) 7.4 Why is the while loop placed in a try-catch structure? (2) Appendix The LinkedQueue class: public class LinkedQueue implements Queue { private Node first, last; private int count; public LinkedQueue() { first = last = null; count =0; } public int size() { return count; } public boolean isEmpty() { return (count == 0); 12 } public void enqueue(Object o) { Node node = new Node(); node.element = o; node.next = null; node.prev = last; if (last != null){ last.next = node; } else { last = first = node; } last = node; count++; } public void dequeue() { if ((first!= null) & (first.next!=null)) { first = first.next; first.prev = null; count--; } else { first = last = null; count--; } } public Object front() { return first; } } class Node { Object element; Node next, prev; } The Stack class: public class Stack { protected Object rep[]; protected int top = -1; protected int size = 0; protected int count = 0; public Stack(int size) { if (size > 0) { this.size = size; rep = new Object[size]; } } public boolean isFull() { return (count == size); } public boolean isEmpty() { return (count == 0); } public int getSize() { return size; } public void push(Object e) { if (e != null && !isFull()) { COS2144/102 13 top++; rep[top] = e; count ++; } } public Object pop() { Object result = null; if (!isEmpty()) { result = rep[top]; top--; count--; } return result; } }
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