小编And*_*suk的帖子

我查看了源代码java.util.HashMap并看到了以下代码:

public Set<K> keySet() {
    Set<K> ks;
    return (ks = keySet) == null ? (keySet = new KeySet()) : ks;
}

(Windows,java版"1.8.0_111")

在我的MacBook上它看起来像这样:

public Set<K> keySet() {
    Set<K> ks = keySet;
    if (ks == null) {
        ks = new KeySet();
        keySet = ks;
    }
    return ks;
}

(MacOs X Sierra,java版"1.8.0_121")

为什么两个变体都声明了局部变量ks？为什么不这样写:

public Set<K> keySet() {
    if (keySet == null) {
        keySet = new KeySet();
    }
    return keySet;
}

要么

public Set<K> keySet() {
    return keySet == null ? (keySet = …