public static int[] removeDuplicates(int[] a) {
        /*
          Please implement this method to
          remove all duplicates from the original array. Retain the order of the elements and
          always retain the first occurrence of the duplicate elements.
          For example, parameter: {2,1,2,3}, result: {2,1,3}
         */
    	
    	// Liste initialisieren
    	List<Integer> list = new ArrayList<Integer>();
    	// in Schleife ber Array iterieren
    	for(int i:a){
    		// falls int noch nicht in Liste --> hinzufgen
    		if(!list.contains(i)){
    			list.add((Integer)i);
    		}
    	}
    	
    	// Ergebnis in Array berfhren
    	int[] result=new int[list.size()];    	
    	for(int i=0;i<list.size();i++){
    		result[i]=list.get(i);
    	}
    	
    	return result;
    	
    }