Java 8 之Optional的簡單使用_2019-10-19

Java 8 之Optional的簡單使用

NPE(NullPointerException)伴隨程序員的一生，優雅是程序員一生的追求

package studyjava;

import java.util.Optional;

/**
 * @author NOknow
 * @version 1.0
 * @CreateDate 2019/10/14
 * @Desc
 */
public class OptionalTest {
    public static void main(String[] args) {
        String nonNullValue = "this is a nonNullValue";
        String nullValue = null;
        String defaultValue1 = Optional.ofNullable(nullValue).orElse("defaultValue1");
        System.out.println(defaultValue1);//defaultValue1

        String defaultValue2 = Optional.ofNullable(nullValue).orElse(getDefaultValue2());
        System.out.println(defaultValue2);//defaultValue2

        String defaultValue3 = Optional.ofNullable(nullValue).orElseGet(() -> getDefaultValue3());
        System.out.println(defaultValue3);//defaultValue3

        //不會打印
        Optional.ofNullable(nullValue).ifPresent(value -> System.out.println("--value is present(not null) : " + value));
        //正常打印  --value is present(not null) : this is a nonNullValue
        Optional.ofNullable(nonNullValue).ifPresent(value -> System.out.println("--value is present(not null) : " + value));

        String tmpValue = Optional.ofNullable(nonNullValue).get();
        System.out.println(tmpValue);//this is a nonNullValue

        //拋異常
        Optional.ofNullable(nullValue)
                .orElseThrow(() -> new RuntimeException("Data is not found in database."));
    }

    private static String getDefaultValue2() {
        return "defaultValue2";
    }

    private static String getDefaultValue3() {
        return "defaultValue3";
    }
}