***Definition:  A key is a value that you are looking for in an array.

The simplest type of search is the sequential search (or linear search).  In the sequential search, each element of the array is compared to the key, in the order it appears in the array, until the desired element is found.  If you are looking for an element that is near the front of the array, the sequential search will find it quickly.  The more data that must be searched, the longer it will take to find the data that matches the key.

Consider this method which will search for a key integer value.  If found, the index (subscript) of the first location of the key will be returned.  If not found, a value of -1 will be returned.

//Find the number of times the name "Jones" appears in an array of names

public static void main(String[] args)
{
    Scanner reply= new Scanner(System.in);
    String key = "Jones"; //case sensitive - "Jones" will not equal "jones"
    String[ ] list = new String [100];   // instantiate the array
    for ( int i=0; i<100; i++)     // fill the array from the keyboard
    {
        System.out.println("Enter name: ");
        list [ i ]=reply.nextLine( );
    }
    int count = search (list, key);    // invoke the method
    System.out.println("Count = " + count);
    reply.close();
}
public static int search(String [ ] list, String key) //method to find "Jones"
{
     int i, count = 0;
     for( i = 0; i< list.length; i++)
     {
          if (list [ i ].equals( key ))
             count = count+1;
     }
     return (count);
} 

// Search for the number 31 in a set of integers
// This search takes place in main.
// This search could also have been placed in a method.
public class BreakBooleanDemo
{
     public static void main(String[ ] args)
     {
           int[ ] numbers = { 12, 13, 2, 33, 23, 31, 22, 6, 87, 16 };
           int key = 31;

           int i = 0;
           boolean found = false;    // set boolean value to false until key is found

          for ( i = 0; i < numbers.length; i++)
          {
                 if (numbers[ i ]  == key)
                {
                         found = true;     
                         break;
                 }
           }

          if (found)   //When found is true, index of location of key is printed.
          {
                System.out.println("Found " + key + " at index " + i + ".");
          }
          else
          {
                System.out.println(key + "is not in this array.");
          }
      }
}

OUTPUT: Found 31 at index 5.