JAVA8新特性(三)——方法引用

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