Java中數組、List、Set互相轉換

數組轉List

String[] staffs = new String[]{"Tom", "Bob", "Jane"}; List staffsList = Arrays.asList(staffs);

• 需要注意的是， Arrays.asList() 返回一個受指定數組決定的固定大小的列表。所以不能做 add 、 remove 等操作，否則會報錯。

  List staffsList = Arrays.asList(staffs);
  staffsList.add("Mary"); // UnsupportedOperationException staffsList.remove(0); // UnsupportedOperationException

• 如果想再做增刪操作呢？將數組中的元素一個一個添加到列表，這樣列表的長度就不固定了，可以進行增刪操作。

  List staffsList = new ArrayList<String>(); for(String temp: staffs){ staffsList.add(temp); } staffsList.add("Mary"); // ok staffsList.remove(0); // ok

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數組轉Set

String[] staffs = new String[]{"Tom", "Bob", "Jane"}; Set<String> staffsSet = new HashSet<>(Arrays.asList(staffs)); staffsSet.add("Mary"); // ok staffsSet.remove("Tom"); // ok

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List轉數組

String[] staffs = new String[]{"Tom", "Bob", "Jane"}; List staffsList = Arrays.asList(staffs); Object[] result = staffsList.toArray();

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List轉Set

String[] staffs = new String[]{"Tom", "Bob", "Jane"}; List staffsList = Arrays.asList(staffs); Set result = new HashSet(staffsList);

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Set轉數組

String[] staffs = new String[]{"Tom", "Bob", "Jane"}; Set<String> staffsSet = new HashSet<>(Arrays.asList(staffs)); Object[] result = staffsSet.toArray();

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Set轉List

String[] staffs = new String[]{"Tom", "Bob", "Jane"}; Set<String> staffsSet = new HashSet<>(Arrays.asList(staffs)); List<String> result = new ArrayList<>(staffsSet);