Java 中的双冒号(::)运算符
双冒号(::)运算符，在 Java 中也称为方法引用运算符，用于借助方法的类直接引用它来调用方法。它们的行为与 lambda 表达式完全一样。它与 lambda 表达式的唯一区别是，它通过名称直接引用方法，而不是向方法提供委托。
语法:
<Class name>::<method name>
示例:要打印流的所有元素:
-
Using Lambda expression:
java stream.forEach( s-> System.out.println(s));程序:
```java // Java code to print the elements of Stream // without using double colon operator
import java.util.stream.*;
class GFG { public static void main(String[] args) {
// Get the stream Stream stream = Stream.of("Geeks", "For", "Geeks", "A", "Computer", "Portal");
// Print the stream stream.forEach(s -> System.out.println(s)); } } ```
Output:
```java Geeks For Geeks A Computer Portal
```
-
Using double colon operator:
java stream.forEach( System.out::println(s));程序:演示双冒号运算符的使用
```java // Java code to print the elements of Stream // using double colon operator
import java.util.stream.*;
class GFG { public static void main(String[] args) {
// Get the stream Stream stream = Stream.of("Geeks", "For", "Geeks", "A", "Computer", "Portal");
// Print the stream // using double colon operator stream.forEach(System.out::println); } } ```
Output:
```java Geeks For Geeks A Computer Portal
```
何时以及如何使用双冒号运算符？
方法引用或双冒号运算符可用于引用:
- 一种静态方法，
- 实例方法，或者
- 一个构造者。
如何在 Java 中使用方法引用:
-
Static method
语法:
java (ClassName::methodName)示例:
java SomeClass::someStaticMethod程序:
```java // Java code to show use of double colon operator // for static methods
import java.util.*;
class GFG {
// static function to be called static void someFunction(String s) { System.out.println(s); }
public static void main(String[] args) {
List list = new ArrayList(); list.add("Geeks"); list.add("For"); list.add("GEEKS");
// call the static method // using double colon operator list.forEach(GFG::someFunction); } } ```
Output:
```java Geeks For GEEKS
```
-
Instance method
语法:
java (objectOfClass::methodName)示例:
java System.out::println程序:
```java // Java code to show use of double colon operator // for instance methods
import java.util.*;
class GFG {
// instance function to be called void someFunction(String s) { System.out.println(s); }
public static void main(String[] args) {
List list = new ArrayList(); list.add("Geeks"); list.add("For"); list.add("GEEKS");
// call the instance method // using double colon operator list.forEach((new GFG())::someFunction); } } ```
Output:
```java Geeks For GEEKS
```
-
Super method
语法:
java (super::methodName)示例:
java super::someSuperClassMethod程序:
```java // Java code to show use of double colon operator // for super methods
import java.util.; import java.util.function.;
class Test {
// super function to be called String print(String str) { return ("Hello " + str + "\n"); } }
class GFG extends Test {
// instance method to override super method @Override String print(String s) {
// call the super method // using double colon operator Function func = super::print;
String newValue = func.apply(s); newValue += "Bye " + s + "\n"; System.out.println(newValue);
return newValue; }
// Driver code public static void main(String[] args) {
List list = new ArrayList(); list.add("Geeks"); list.add("For"); list.add("GEEKS");
// call the instance method // using double colon operator list.forEach(new GFG()::print); } } ```
Output:
```java Hello Geeks Bye Geeks
Hello For Bye For
Hello GEEKS Bye GEEKS
```
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