int x;
x = 10;

Integer num;
num = new Integer(10);

public void doSomething(Integer num){
   //do something to num
}

doSomething(null);

public void doSomething(Integer num){
    if(num != null){
       //do something to num
    }
}

public class Example
{
    public static void main(String[] args)
    {
        Object obj = null;
        obj.hashCode();
    }
}

public class Printer {
    private String name;

    public void setName(String name) {
        this.name = name;
    }

    public void print() {
        printString(name);
    }

    private void printString(String s) {
        System.out.println(s + " (" + s.length() + ")");
    }

    public static void main(String[] args) {
        Printer printer = new Printer();
        printer.print();
    }
}

Exception in thread "main" java.lang.NullPointerException
    at Printer.printString(Printer.java:13)
    at Printer.print(Printer.java:9)
    at Printer.main(Printer.java:19)

private String name = "";

printString((name == null) ? "" : name);

public class Printer {
    private final String name;

    public Printer(String name) {
        this.name = Objects.requireNonNull(name);
    }

    public void print() {
        printString(name);
    }

    private void printString(String s) {
        System.out.println(s + " (" + s.length() + ")");
    }

    public static void main(String[] args) {
        Printer printer = new Printer("123");
        printer.print();
    }
}

public class Test {
        public static void main(String[] args) {
            String foo = null;
            int length = foo.length();   // HERE
        }
    }

$ javac Test.java
$ java Test
Exception in thread "main" java.lang.NullPointerException
    at Test.main(Test.java:4)
$

Exception in thread "main" java.lang.NullPointerException

at Test.main(Test.java:4)

int length = foo.length(); // HERE

public class Test {

    private static String[] foo = new String[2];

    private static int test(String[] bar, int pos) {
        return bar[pos].length();
    }

    public static void main(String[] args) {
        int length = test(foo, 1);
    }
}

$ javac Test.java
$ java Test
Exception in thread "main" java.lang.NullPointerException
    at Test.test(Test.java:6)
    at Test.main(Test.java:10)
$

return args[pos].length();

int length = test(foo, 1);

private static String[] foo = new String[2];

String a = null;
System.out.println(a.toString()); // NullPointerException will be thrown

public class Some {
    private int id;
    public int getId(){
        return this.id;
    }
    public setId( int newId ) {
        this.id = newId;
    }
}
....
....
// Somewhere else...
Some reference = new Some();    // Point to a new object of type Some()
Some otherReference = null;     // Initiallly this points to NULL

reference.setId( 1 );           // Execute setId method, now private var id is 1

System.out.println( reference.getId() ); // Prints 1 to the console

otherReference = reference      // Now they both point to the only object.

reference = null;               // "reference" now point to null.

// But "otherReference" still point to the "real" object so this print 1 too...
System.out.println( otherReference.getId() );

// Guess what will happen
System.out.println( reference.getId() ); // :S Throws NullPointerException because "reference" is pointing to NULL remember...

public class student {
    private int id;
    public int getId(){
        return this.id;
    }
    public setId( int newId ) {
        this.id = newId;
    }
}

public class School
{

   student Obj_Student;
   public school()
   {

      try
      {

         Obj_Student.getId();
      }catch(Exception e)
      {
           System.out.println("Null Pointer ");
      }
   }

}

public class School
    {

       student Obj_Student;
       public school()
       {

          try
          {
             Obj_Student = new student();
             Obj_Student.setId(12);
             Obj_Student.getId();
          }catch(Exception e)
          {
               System.out.println("Null Pointer ");
          }
       }

    }

String[] phrases = new String[10];
String keyPhrase = "Bird";
for(String phrase : phrases) {
    System.out.println(phrase.equals(keyPhrase));
}

String[] phrases = new String[] {"The bird", "A bird", "My bird", "Bird"};
String keyPhrase = "Bird";
for(String phrase : phrases) {
    System.out.println(phrase.equals(keyPhrase));
}