java8中:: 用法示例（JDK8双冒号用法）

public class AcceptMethod {
 
 public static void printValur(String str){
 System.out.println("print value : "+str);
 }
 
 public static void main(String[] args) {
 List al = Arrays.asList("a","b","c","d");
 for (String a: al) {
  AcceptMethod.printValur(a);
 }
 //下面的for each循环和上面的循环是等价的 
 al.forEach(x->{
  AcceptMethod.printValur(x);
 });
 }
}

public class MyTest {
 public static void printValur(String str){
 System.out.println("print value : "+str);
 }
 
 public static void main(String[] args) {
 List al = Arrays.asList("a", "b", "c", "d");
 al.forEach(AcceptMethod::printValur);
 //下面的方法和上面等价的
 Consumer methodParam = AcceptMethod::printValur; //方法参数
 al.forEach(x -> methodParam.accept(x));//方法执行accept
 }
}

/**
 * Performs the given action for each element of the {@code Iterable}
 * until all elements have been processed or the action throws an
 * exception. Unless otherwise specified by the implementing class,
 * actions are performed in the order of iteration (if an iteration order
 * is specified). Exceptions thrown by the action are relayed to the
 * caller.
 *
 * @implSpec
 * <p>The default implementation behaves as if:
 * <pre>{@code
 * for (T t : this)
 *  action.accept(t);
 * }</pre>
 *
 * @param action The action to be performed for each element
 * @throws NullPointerException if the specified action is null
 * @since 1.8
 */
 default void forEach(Consumer<? super T> action) {
 Objects.requireNonNull(action);
 for (T t : this) {
  action.accept(t);
 }
 }