1、函数式编程；
2、第一次get时才会初始化；
3、可以实现单例或缓存。
package suppliers; import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.common.collect.Iterables; import java.util.ServiceLoader; /**
* @author xfyou
* @date 2018/7/30
*/
public class Test { public static void main(String[] args) {
try {
//shouldInitTheSupplierWrappedObjectWhenGetObject();
shouldInitTheSupplierWrappedObjectForOnlyOneTime();
} catch (Exception e) {
e.printStackTrace();
}
} private static void shouldInitTheSupplierWrappedObjectWhenGetObject() throws Exception {
Supplier<Integer> memoize = Suppliers.memoize(new Supplier<Integer>() {
@Override
public Integer get() {
System.out.println("init supplier wrapped object");
return 1;
}
});
System.out.println("main thread block");
Thread.sleep(2000);
System.out.println(memoize.get());
System.out.println(memoize.get());
} private static void shouldInitTheSupplierWrappedObjectForOnlyOneTime() {
Supplier<Admin> memoize = Suppliers.memoize(new Supplier<Admin>() {
@Override
public Admin get() {
System.out.println("init supplier wrapped object");
ServiceLoader<Admin> loader = ServiceLoader.load(Admin.class);
return Iterables.getFirst(loader, null);
}
});
System.out.println(memoize.get());
System.out.println(memoize.get());
System.out.println(memoize.get());
}
}
package suppliers; /**
* @author xfyou
* @date 2018/7/31
*/
public interface User {
/**
* @param firstName
* @param lastName
*/
void addUser(String firstName, String lastName);
}
package suppliers; import lombok.ToString; import java.util.concurrent.atomic.AtomicReference; /**
* @author xfyou
* @date 2018/7/31
*/
@ToString
public class Admin implements User {
private static final AtomicReference<Admin> INSTANCE = new AtomicReference<>(); public Admin() {
if (!INSTANCE.compareAndSet(null, this)) {
throw new IllegalStateException("This class only can be initialized once");
} else {
System.out.println("Construct");
}
} @Override
public void addUser(String firstName, String lastName) {
System.out.println("Add new user");
}
}