将`Arrays.stream(...).collect(...)`从Java 8转换为Java 7

Question

如何转换这段代码:

private static Map<CustomObj<? extends CustomOtherObj>, CustomEnumeration> map;
    if (map == null) {
        map = Arrays.stream(CustomEnumeration.values())
            .collect(Collectors.toMap(x -> x.source, x -> x));
    }

进入Java 7等价？(Arrays.stream.collect(Collectors....)部分.

基本上,上面的代码将一些元素放在地图中.

Answer 1

非常简单

if (map == null) {
    map = new HashMap<>();
    for(CustomEnumeration e : CustomEnumeration.values())
        map.put(e.source, e);
}