ion、 SequencedMap 接口,为我们执行一些顺序性操作比如获取头尾值提供了各类接口方法
继承关系如下图所示:
接口定义如下
interface SequencedCollection<E> extends Collection<E> {
// new method
SequencedCollection<E> reversed();
// methods promoted from Deque
void addFirst(E);
void addLast(E);
E getFirst();
E getLast();
E removeFirst();
E removeLast();
}
interface SequencedSet<E> extends Set<E>, SequencedCollection<E> {
SequencedSet<E> reversed(); // covariant override
}
interface SequencedMap<K,V> extends Map<K,V> {
// new methods
SequencedMap<K,V> reversed();
SequencedSet<K> sequencedKeySet();
SequencedCollection<V> sequencedValues();
SequencedSet<Entry<K,V>> sequencedEntrySet();
V putFirst(K, V);
V putLast(K, V);
// methods promoted from NavigableMap
Entry<K, V> firstEntry();
Entry<K, V> lastEntry();
Entry<K, V> pollFirstEntry();
Entry<K, V> pollLastEntry();
}
Record Patterns (记录模式)-JEP 440
这个更新主要简化了类型判断与赋值的使用,类型判断后无需显式强制转换且如果模式匹配,变量被初始化为要匹配的模板值, 这个说起来比较拗口,结合代码大家理解下,我感觉还是挺有用的,这里我把JDK8 JDK17 JDK21 的实现进行一个对比,大家就明白了。
// As of Java 8
record Point(int x, int y) {}
static void printSum(Object obj) {
if (obj instanceof Point) {
Point p = (Point) obj;
int x = p.x();
int y = p.y();
System.out.println(x+y);
}
}
// As of Java 16
record Point(int x, int y) {}
static void printSum(Object obj) {
if (obj instanceof Point p) {
int x = p.x();
int y = p.y();
System.out.println(x+y);
}
}
// As of Java 21
static void printS