我们之前写Lambda表达式,如果Lambda表达式有对应方法,我们可以直接引用方法作为Lambda表达式。这种做法叫做方法引用。方法引用用”::”分隔。
例子
@Test public void methodRefTest() { MethodReference.Class1 class1 = new MethodReference.Class1(); double result = doubleUnatuOperator(4.5, class1::return1); System.out.println("result:" + result); } public double doubleUnatuOperator(double num, DoubleUnaryOperator doubleUnaryOperator) { return doubleUnaryOperator.applyAsDouble(num); } static class Class1 { public double return1(double i) { return 1 + i; } }
这里doubleSupplier的表达式调用Class1.return1方法,就可以使用方法引用。
方法引用有四种
引用静态方法
ContainingClass::staticMethodName
例子: String::valueOf,对应的Lambda:(s) -> String.valueOf(s)
比较容易理解,和静态方法调用相比,只是把.换为::
引用特定对象的实例方法
containingObject::instanceMethodName
例子: x::toString,对应的Lambda:() -> this.toString()
与引用静态方法相比,都换为实例的而已
引用构造函数
ClassName::new
例子: String::new,对应的Lambda:() -> new String()
构造函数本质上是静态方法,只是方法名字比较特殊。
引用特定类型的任意对象的实例方法
这个不清楚
例子
public class MethodReference { @Test public void staticMethodRefTest() { double result = doubleUnatuOperator(4.5, Class1::staticReturn1); System.out.println("result:" + result); } @Test public void methodRefTest() { MethodReference.Class1 class1 = new MethodReference.Class1(); double result = doubleUnatuOperator(4.5, class1::return1); System.out.println("result:" + result); } @Test public void constructorRefTest() { Class1 class1 = supplier(Class1::new); System.out.println(class1); } @Test public void ContainingTypeRefTest() { String[] stringArray = {"Barbara", "James", "Mary", "John", "Patricia", "Robert", "Michael", "Linda"}; Arrays.sort(stringArray, (a, b) -> { return a.compareToIgnoreCase(b); }); System.out.println(Arrays.toString(stringArray)); Arrays.sort(stringArray, String::compareToIgnoreCase); System.out.println(Arrays.toString(stringArray)); } public static double doubleUnatuOperator(double num, DoubleUnaryOperator doubleUnaryOperator) { return doubleUnaryOperator.applyAsDouble(num); } public Object unaryOperator(Object t,UnaryOperator<Object> operator) { return operator.apply(t); } public Class1 supplier(Supplier<Class1> supplier) { return supplier.get(); } static class Class1 { private String name; public String getName() { return name; } public void setName(String name) { this.name = name; } public Class1() { } public Class1(String name) { System.out.println(name + "构造成功"); } public double return1(double i) { return 1 + i; } public static double staticReturn1(double i) { return i + 1; } public double add(Class1 a) { return 12.0; } @Override public String toString() { return "Class1{" + "name='" + name + '\'' + '}'; } } }