java - How can I subtract from arraylist some values ? -

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here example: 

public static arraylist<integer> position = new arraylist<integer>(); public static arraylist<integer> new_position = new arraylist<integer>();  collections.copy(new_position, position);     (int j = 0; j < position.size(); j++) {          new_position.get(j) -=4;     }

i want copy values , new arraylist subtract 4. how can make ? i'm new in java. i've got error such as: the left-hand side of assignment must variable, refers nowe_pozycje.get(j) -=4;.

you have get() value, change it, , set() new value: 

for (int j = 0; j < position.size(); j++) {     new_position.set(j, new_position.get(j) - 4); }

an alternative solution skip whole copying of list, , instead iterate through original list, change each value go, , add them new list: 

public static arraylist<integer> new_position = new arraylist<integer>(); (integer i: position) {     new_position.add(i - 4); }

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