Lambda表示式--Java8的新功能案例詳解(2) Lambda表示式的方法引用
Lambda表示式與內部類相比有很多限制，比如只能為函式式介面建立例項，但是Lambda表示式大大簡化了程式碼的書寫。
Lambda表示式的方法引用主要分為下面幾類：
1.引用類方法2.引用特定物件的例項方法
3.引用某類物件的例項方法
4.引用構造方法
下面通過幾個例項演示了這幾種方法引用的：
1.首先建立下面的介面
/* 該函式式介面只包含一個抽象方法convert——用於將String型別的引數轉換為Intege型別的返回值 */ @FunctionalInterface interface Converter { Integer convert(String from); } /* 函式式介面，根據3個引數產生一個String型別的返回值 */ @FunctionalInterface interface MakeString { String make(String a,int b,int c); } /* 函式式介面，根據輸入的title返回一個JFrame物件 */ @FunctionalInterface interface GetJFrame { javax.swing.JFrame get(String title); }
2.
/* Lambda表示式的方法引用 1.引用類方法 2.引用特定物件的例項方法 3.引用某類物件的例項方法 4.引用構造方法 5.使用Lambda表示式呼叫Arrays類的方法 */ public class MethodRefer { public static void main(String[] args) { //-------------------------------------------1.引用類方法----------------------------------------------- /* 使用Lambda表示式建立Converter物件 由於ambda表示式只有一個引數、一條語句和一個返回值， 因此可以省略引數的小括號、語句的花括號和返回值的return關鍵字 */ Converter con_1=from->Integer.valueOf(from); /* 方法引用代替Lambda表示式：引用類方法 函式式介面中被實現方法的全部引數傳給該類方法作為引數 */ Converter con_2=Integer::valueOf; Integer val1=con_1.convert("111111"); Integer val2=con_2.convert("222222"); System.out.println(val1); System.out.println(val2); //---------------------------------------2.引用特定物件的例項方法----------------------------------------- //呼叫String類的indexOf方法建立物件 Converter con_4="sharejava"::indexOf; Integer val4=con_4.convert("java"); Converter con_3=from->"sharejava".indexOf(from); Integer val3=con_3.convert("java"); System.out.println(val4); System.out.println(val3); //---------------------------------------3.引用某類物件的例項方法----------------------------------------- MakeString ms1=(a,b,c)->a.substring(b,c); String str1=ms1.make("sharejava",5,9); MakeString ms2=String::substring; String str2=ms2.make("sharejava",5,9); System.out.println(str1); System.out.println(str2); //---------------------------------------4.引用構造方法----------------------------------------- GetJFrame g1=title->new javax.swing.JFrame(title); javax.swing.JFrame jf1=g1.get("我的視窗"); GetJFrame g2=javax.swing.JFrame::new; javax.swing.JFrame jf2=g2.get("我的視窗"); jf1.setVisible(true); jf1.setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE ); jf1.setBounds(200,200,500,400); } }
3.使用Lambda表示式呼叫Arrays類的方法
我們發現Arrays類的API下包含大量的方法需要函式式介面引數：
static void parallelPrefix(double[] array, DoubleBinaryOperator op)
Cumulates, in parallel, each element of the given array in place, using the supplied function.
static void parallelPrefix(double[] array, int fromIndex, int toIndex, DoubleBinaryOperator op)
Performs parallelPrefix(double[], DoubleBinaryOperator) for the given subrange of the array.
static void parallelPrefix(int[] array, IntBinaryOperator op)
Cumulates, in parallel, each element of the given array in place, using the supplied function.
static void parallelPrefix(int[] array, int fromIndex, int toIndex, IntBinaryOperator op)
Performs parallelPrefix(int[], IntBinaryOperator) for the given subrange of the array.
static void parallelPrefix(long[] array, int fromIndex, int toIndex, LongBinaryOperator op)
Performs parallelPrefix(long[], LongBinaryOperator) for the given subrange of the array.
static void parallelPrefix(long[] array, LongBinaryOperator op)
Cumulates, in parallel, each element of the given array in place, using the supplied function.
static <T> void parallelPrefix(T[] array, BinaryOperator<T> op)
Cumulates, in parallel, each element of the given array in place, using the supplied function.
static <T> void parallelPrefix(T[] array, int fromIndex, int toIndex, BinaryOperator<T> op)
Performs parallelPrefix(Object[], BinaryOperator) for the given subrange of the array.
static void parallelSetAll(double[] array, IntToDoubleFunction generator)
Set all elements of the specified array, in parallel, using the provided generator function to compute each element.
static void parallelSetAll(int[] array, IntUnaryOperator generator)
Set all elements of the specified array, in parallel, using the provided generator function to compute each element.
static void parallelSetAll(long[] array, IntToLongFunction generator)
Set all elements of the specified array, in parallel, using the provided generator function to compute each element.
static <T> void parallelSetAll(T[] array, IntFunction<? extends T> generator)
Set all elements of the specified array, in parallel, using the provided generator function to compute each element.
static <T> void parallelSort(T[] a, Comparator<? super T> cmp)
Sorts the specified array of objects according to the order induced by the specified comparator.
static <T extends Comparable<? super T>> void parallelSort(T[] a, int fromIndex, int toIndex)
Sorts the specified range of the specified array of objects into ascending order, according to the natural ordering of its elements.
static <T> void parallelSort(T[] a, int fromIndex, int toIndex, Comparator<? super T> cmp)
Sorts the specified range of the specified array of objects according to the order induced by the specified comparator.
static void setAll(double[] array, IntToDoubleFunction generator)
Set all elements of the specified array, using the provided generator function to compute each element.
static void setAll(int[] array, IntUnaryOperator generator)
Set all elements of the specified array, using the provided generator function to compute each element.
static void setAll(long[] array, IntToLongFunction generator)
Set all elements of the specified array, using the provided generator function to compute each element.
static <T> void setAll(T[] array, IntFunction<? extends T> generator)
Set all elements of the specified array, using the provided generator function to compute each element.
這裡演示了其中部分方法的應用：
import java.util.Arrays;
public class LambdaArrays
{
public static void main(String[] args)
{
String[] arr1=new String[]{"html","c#","c","c++","java"};
//目標型別是Comparator根據字串的長度判斷字串的大小，然後排序
Arrays.parallelSort(arr1,(o1,o2)->o1.length()-o2.length());
System.out.println(Arrays.toString(arr1));
int[] arr2=new int[]{-9,1,5,-4,12};
//目標型別是 IntBinaryOperator，根據前後兩個元素計算當前元素的值
Arrays.parallelPrefix(arr2,(left,right)->left*right);
System.out.println(Arrays.toString(arr2));
}
}