The Java supports primitive data type boolean, which can be used as return type.
Example: The following program uses a method that returns boolean value true or false depending on whether a given positive integer number greater than 2 is prime or not.
1 class CheckPrime
2 { static boolean checkPrime(int number)
3 { int root = (int) Math.sqrt(number);
4 for(int i = 2; i <= root; i++)
5 { if( number % i = = 0)
6 return false;
7 }
8 return true;
9 }
10 public static void main(String a[])
11 { int n = Integer.parseInt(a[0]);
12 boolean prime = checkPrime(n);
13 if(prime)
14 System.out.println("The number " + n + " is prime");
15 else
16 System.out.println("The number " + n + " is not prime");
17 }
18 }
13. Examples
Example: The following example shows the static implementation (using array) of stack.
1 class Stack
2 { private int top = -1;
3 private int a[] = new int[10];
4 void push(int x)
5 { if(top == 9)
6 { System.out.println("Stack Full");
7 return;
8 }
9 top = top + 1;
10 a[top] = x;
11 }
12 int pop()
13 { if(top == -1)
14 { System.out.println("Stack Empty");
15 return -1; //assuming that -1 is not a valid data
16 }
17 int x = a[top]; top = top - 1;
18 return x;
19 }
20 }
class StackDemo
1 { public static void main(String args[])
2 { Stack s1 = new Stack();
3 Stack s2 = new Stack();
4 for(int i = 0; i < 10; i++)
5 { s1.push(i);
6 }
7 for(int i = 10; i < 20; i++)
8 { s2.push(i);
9 }
10 int x;
11 for(int i = 0; i < 10; i++)
12 { x = s1.pop();
13 System.out.print(x + " ");
14 }
15 System.out.println();
16 for(int i = 0; i < 10; i++)
17 { x = s2.pop();
18 System.out.print(x + " ");
19 }
20 }
Output:
9 8 7 6 5 4 3 2 1 0
19 18 17 16 15 14 13 12 11 10
Example: The following example demonstrates that only one copy per class is created in case of static members. Thus the implementation is not correct if data member top and a[] are declared to be static as in that case all the objects of Stack class will share the same memory.
1 class Stack
2 { static int top = -1;
3 static int a[] = new int[10];
4 static void push(int x)
5 { if(top == 9)
6 { System.out.println("Stack Full");
7 return;
8 }
9 top = top + 1;
10 a[top] = x;
11 }
12 static int pop()
13 { if(top == -1)
14 { System.out.println("Stack Empty");
15 return -1; //assuming that -1 is not a valid data
16 }
17 int x = a[top];
18 top = top - 1;
19 return x;
20 }
21 }
1 class StackDemo
2 { public static void main(String args[])
3 { Stack s1 = new Stack();
4 Stack s2 = new Stack();
5 for(int i = 0; i < 10; i++)
6 { s1.push(i);
7 }
8 for(int i = 10; i < 20; i++)
9 { s2.push(i);
10 }
11 int x;
12 for(int i = 0; i < 10; i++)
13 { x = s1.pop();
14 System.out.print(x + " ");
15 }
16 System.out.println();
17 for(int i = 0; i < 10; i++)
18 { x = s2.pop();
19 System.out.print(x + " ");
20 }
21 }
22 }
Output:
Stack Full
Stack Full
Stack Full
Stack Full
Stack Full
Stack Full
Stack Full
Stack Full
Stack Full
Stack Full
9 8 7 6 5 4 3 2 1 0
Stack Empty
-1 Stack Empty
-1 Stack Empty
-1 Stack Empty
-1 Stack Empty
-1 Stack Empty
-1 Stack Empty
-1 Stack Empty
-1 Stack Empty
-1 Stack Empty
-1
Example: The following example shows the dynamic implementation (using linked list) of stack.
1 class Node
2 { Node nextNode;
3 int x;
4 }
1 class Stack
2 { Node top;
3 void push(int item)
4 { Node temp;
5 if(top == null)
6 { top = new Node();
7 top.x = item; top.nextNode = null;
8 }
9 else
10 { temp = new Node();
11 temp.x = item;
12 temp.nextNode = top;
13 top = temp;
14 }
15 }
16 int pop()
17 { if(top == null)
18 { System.out.println("Stack is empty");
19 return(-1);
20 }
21 else
22 { int x = top.x; top = top.nextNode;
23 return x;
24 }
25 }
26 }
1 class StackTest
2 { static public void main(String args[])
3 { Stack st = new Stack();
4 st.pop();
5 for(int i = 0; i < 5; i++)
6 st.push(i);
7 for(int i = 0; i <= 5; i++)
8 System.out.println(st.pop());
9 }
10 }
Output:
Stack is empty
4
3
2
1
0
Stack is empty
-1