我不太清楚我是否理解Oracle Java教程中的Lambda表達式教程。令我困惑的主要是lambda的Index參數。 ds.print(index ->{...}
編譯器如何知道甚至是什麼值索引?索引沒有在程序中的其他地方聲明,那麼索引參數究竟是什麼引用以及編譯器如何知道?瞭解Lambda表達式
Excerise問題:
public class DataStructure {
private final static int SIZE = 15;
private int[] arrayOfInts = new int[SIZE];
public DataStructure() {
for (int i = 0; i < SIZE; i++) {
arrayOfInts[i] = i;
}
}
public int size() {
return SIZE;
}
public int get(int index) {
return arrayOfInts[index];
}
interface DataStructureIterator extends java.util.Iterator<Integer> { }
private class EvenIterator implements DataStructureIterator {
private int nextIndex = 0;
public boolean hasNext() {
return (nextIndex <= SIZE - 1);
}
public Integer next() {
Integer retValue = Integer.valueOf(arrayOfInts[nextIndex]);
nextIndex += 2;
return retValue;
}
}
public DataStructureIterator getEvenIterator() {
return new EvenIterator();
}
public void printEven() {
DataStructureIterator iterator = getEvenIterator();
while (iterator.hasNext()) {
System.out.print(iterator.next() + " ");
}
System.out.println();
}
public void print(DataStructureIterator iterator) {
while (iterator.hasNext()) {
System.out.print(iterator.next() + " ");
}
System.out.println();
}
public void print(java.util.function.Function<Integer, Boolean> function) {
for (int i = 0; i < SIZE; i++) {
if (function.apply(i)) {
System.out.print(arrayOfInts[i] + " ");
}
}
System.out.println();
}
public static Boolean isEvenIndex(Integer index) {
if (index % 2 == 0) return Boolean.TRUE;
return Boolean.FALSE;
}
public static Boolean isOddIndex(Integer index) {
if (index % 2 == 0) return Boolean.FALSE;
return Boolean.TRUE;
}
public static void main(String s[]) {
DataStructure ds = new DataStructure();
System.out.println("printEven()");
ds.printEven();
System.out.println("print(DataStructureIterator) with "
+ "getEvenIterator");
ds.print(ds.getEvenIterator());
System.out.println("print(DataStructureIterator) with "
+ "anonymous class, odd indicies");
ds.print(
new DataStructure.DataStructureIterator() {
private int nextIndex = 1;
public boolean hasNext() {
return (nextIndex <= ds.size() - 1);
}
public Integer next() {
int retValue = ds.get(nextIndex);
nextIndex += 2;
return retValue;
}
}
);
System.out.println("print(Function) with lambda expressions");
ds.print(index -> {
if (index % 2 == 0) return Boolean.TRUE;
return Boolean.FALSE;
});
ds.print(index -> {
if (index % 2 == 0) return Boolean.FALSE;
return Boolean.TRUE;
});
System.out.println("print(Function) with method references");
ds.print(DataStructure::isEvenIndex);
ds.print(DataStructure::isOddIndex);
}
}
的Java現在使用類型Intereface即它看起來什麼表達式返回以及如何表達來確定它的類型。 –