if...else if-...-else 

You can use this form to avoid creating nested blocks and make the code easier to read and understand. For example, look at the following code snippet:

  if(n > 5){
    System.out.println("n > 5");
  } else {
    if (n == 5) {
      System.out.println("n == 5");
    } else {
      if (n == 4) {
        System.out.println("n == 4");
      } else {
        System.out.println("n < 4");
      }
    }
  }
}

These nested if...else statements can be replaced by if...else...if statements as follows:

if(n > 5){
  System.out.println("n > 5");
} else if (n == 5) {
  System.out.println("n == 5");
} else if (n == 4) {
  System.out.println("n == 4");
} else {
  System.out.println("n < 4");
}

Such code is easier to read and understand.

If you don't need to do anything when n < 4, you can leave out the last catch-all-the-rest-options else clause:

if(n > 5){
  System.out.println("n > 5");
} else if (n == 5) {
  System.out.println("n == 5");
} else if (n == 4) {
  System.out.println("n == 4");
} 

If you need to do something for each particular value, you can write, for example: 

if(x == 5){
  //do something
} else if (x == 7) {
  //do something else
} else if (x == 12) {
  //do something different
} else if (x = 50) {
  //do something yet more different
} else {
  //do something completely different
}

But there is a dedicated selection statement for such cases, called switch...case, which is easier to read and understand.