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 + '\'' +
'}';
}
}
}