Java Array, Finding Duplicates

I have an array, and am looking for duplicates.

duplicates = false;
for(j = 0; j < zipcodeList.length; j++){
    for(k = 0; k < zipcodeList.length; k++){
        if (zipcodeList[k] == zipcodeList[j]){
            duplicates = true;
        }
    }
}

However, this code doesnt work when there are no duplicates. Whys that?