Generics

1. List oznacza każdą listę czegokolwiek
2. List foo = new ArrayList();// bad!
3. 1) List list = new ArrayList(); //OK
   2) List aList = new ArrayList();//OK
   3) List foo = new ArrayList(); //BAD
   4) List cList = new ArrayList();//BAD
   5) List bList = new ArrayList(); //OK
   6) List dList = new ArrayList(); //BAD
   

equal i hashCode

1. int hashcode() - jaki bukiet ?
2. boolean equals(Object ob)
3. sprawdzaj na początku instanceof!
4. nie używaj transient zmiennych w hashCode()

   @Test
   public void test1() {

       NotEqualOverriding a = new NotEqualOverriding();
       NotEqualOverriding b = new NotEqualOverriding();

       a.equals(b); //wersja 1 z return false;
       a.equals((Object)b); //wersja 2

 
   }

   class NotEqualOverriding{

      /*Tylko overloading*/
      boolean equals(NotEqualOverriding er){
          return false;
      }
      /**  -> zonk to jest overloading!  */
     // @Override

      public boolean equals(Object obj) {
          // dodaj na poczatku test is-A!!
         System.out.println(" nadpisny equal");
          return super.equals(obj);
      }

      @Override
      public int hashCode() {
          int hash = 7;
          return hash;
      }
   }

Try, catch throwing Exception

    @Test
    public void testThrowing(){
       try{  }catch(NumberFormatException ex){ }finally{   }
    }
    
    @Test
    public void testThrowing2() throws Exception{
       try{
           throw  new Exception(); //=> musi byc throws
       }catch(NumberFormatException ex){
            throw new Exception();
            //int x =9; // unreachable exception!!!!!!!!
       }finally{
           /**
            * Wypisze naewt jak jest w Main;
            */
           System.out.println("finally"); //wypisze
       }
    }

Porównanie integerów

    @Test
    public void testone(){

        //test1
        Integer piec1= 5;
        Integer piec2= 5;
        assertTrue(piec1==piec2); //pass

        //test2
        Integer integer1 = new Integer(10);
        Integer integer2 = new Integer(10);
        assertFalse(integer1==integer2); //pass

        //test3
        Integer piec1001= 1000;
        Integer piec1002= 1000;
        assertTrue(piec1==piec2); //pass
  
    }

Linki

1. http://mocktestscjp.blogspot.com/
2. http://www.indijava.in/community/tips/scjp_pitfalls
3. http://technoheads.blogspot.com/
4. http://faq.javaranch.com/java/ScjpMockTests
   

class A{
public static void metoda(){}
public void metoda{}
}

Błąd bo te samy nazwy metod mimo ,że jedna jest static!

Autoboxing

//LEGAL
long l = 1000;
double d = 1000;

//NOT LEGAL
Long l1 = 1000; // error
Double d1 = 1000; // error

i

    private static void wrap_byte(Byte b) {}  
    private static void wrap_short(Short s) {}  
    private static void wrap_char(Character c) {}  
    private static void wrap_int(Integer i) {}  
    private static void wrap_long(Long l) {}  
    private static void wrap_float(Float f) {}  
    private static void wrap_double(Double d) {} 

    private static void print() {  
        wrap_byte(10);   // error         
        wrap_short(10);   // error  
        wrap_char(10);   // error  
        wrap_int(10);  
        wrap_long(10);   // error  
        wrap_float(10);   // error  
        wrap_double(10);   // error  
    }