Google Guava学习（1）-Guava Optional类

package com.example.google.guava.demo.clazz;

import com.google.common.base.Optional;

/**
* <p>
* <code>OptionalTest</code>
* </p>
* Description:输出结果
* > First parameter is present: false
* > Second parameter is present: true
* > 10
*
* @author Mcchu
* @date 2017/10/18 15:02
*/
public class OptionalTest {

public static void main(String[] args) {
OptionalTest test = new OptionalTest();

Integer value1 = null;
Integer value2 = 10;

// 允许传null
Optional<Integer> a1 = Optional.fromNullable(value1);   //输出：Optional.absent()
//Optional<Integer> a2 = Optional.fromNullable(value2);   //输出：Optional.of(10)

// java.util.Optional<T> 是java8新增
//java.util.Optional<Integer> b1 = java.util.Optional.ofNullable(value1);  //输出：Optional.empty
//java.util.Optional<Integer> b2 = java.util.Optional.ofNullable(value2);  //输出：Optional[10]

// 传null抛NPE
//Optional<Integer> c1 = Optional.of(value1);     //输出：java.lang.NullPointerException
Optional<Integer> c2 = Optional.of(value2);     //输出：Optional.of(10)

Integer result = sum(a1,c2);
System.out.println(result);     //输出：10
}

private static Integer sum(Optional<Integer> a,Optional<Integer> b){
// 判断a、b是否出现（英文翻译：present：出现；absent：未出现，缺席）
System.out.println("First parameter is present: " + a.isPresent());     //输出：false
System.out.println("Second parameter is present: " + b.isPresent());    //输出：true

// 如果值存在，则返回初始值，否则返回默认值，or()方法中是默认值
Integer d1 = a.or(0);   //输出：0
//Integer d2 = b.or(0);   //输出：10

//Integer e1 = a.get();   //输出：java.lang.IllegalStateException: Optional.get() cannot be called on an absent value
Integer e2 = b.get();   //输出：10

return d1 + e2;
}
}

First parameter is present: false
Second parameter is present: true
10