Topological sorting is a linear ordering of vertices such that for every directed edge ij, vertex i comes before j in the ordering.

Topological sorting is only possible for Directed Acyclic Graph (DAG).

Applications:

jobs scheduling from the given dependencies among jobs.

ordering of formula cell evaluation in spreadsheets

ordering of compilation tasks to be performed in make files,

data serialization

resolving symbol dependencies in linkers.

Topological Sort Code in Java:

```
// V - total vertices
// visited - boolean array to keep track of visited nodes
// graph - adjacency list.
// Main Topological Sort Function.
void topologicalSort()
{
Stack<Integer> stack = new Stack<Integer>();
// Mark all the vertices as not visited
boolean visited[] = new boolean[V];
for (int j = 0; j < V; j++){
visited[j] = false;
}
// Call the util function starting from all vertices one by one
for (int i = 0; i < V; i++)
if (visited[i] == false)
topologicalSortUtil(i, visited, stack);
// Print contents of stack -> result of topological sort
while (stack.empty() == false)
System.out.print(stack.pop() + " ");
}
// A helper function used by topologicalSort
void topologicalSortUtil(int v, boolean visited[],
Stack<Integer> stack)
{
// Mark the current node as visited.
visited[v] = true;
Integer i;
// Recur for all the vertices adjacent to the current vertex
Iterator<Integer> it = graph.get(v).iterator();
while (it.hasNext()) {
i = it.next();
if (!visited[i])
topologicalSortUtil(i, visited, stack);
}
// Push current vertex to stack that saves result
stack.push(new Integer(v));
}
```