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Optional类是Java8为了解决null值判断问题，使用Optional类可以避免显式的null值判断（null的防御性检查），避免null导致的NPE（NullPointerException）。

示例：

public static void main(String[] args) {
	TestDemo testDemo = new TestDemo();
	getCount(testDemo);
}

private static void getCount(TestDemo testDemo) {
	//if判断：判断好多层
	int count1 = 1;
	if(testDemo != null){
		if(testDemo.getCount() != null){
			count1 = testDemo.getCount();
		}
	}
	System.out.println(count1);
	
	//三目运算符：嵌套层数深，可读性不好
	int count2 = testDemo != null ? (testDemo.getCount() != null ? testDemo.getCount() : 1) : 1;
	System.out.println(count2);
	
	//Java8-Optional：优雅，可读性较好
	int count3 = Optional.ofNullable(testDemo).map(item -> item.getCount()).orElse(1);
	System.out.println(count3);
}

private static class TestDemo {

	private Integer count;

	public Integer getCount() {
		return count;
	}

	public void setCount(Integer count) {
		this.count = count;
	}
}

源码：

/**
 * Returns an {@code Optional} describing the specified value, if non-null,
 * otherwise returns an empty {@code Optional}.
 *
 * @param <T> the class of the value
 * @param value the possibly-null value to describe
 * @return an {@code Optional} with a present value if the specified value
 * is non-null, otherwise an empty {@code Optional}
 */
public static <T> Optional<T> ofNullable(T value) {
	return value == null ? empty() : of(value);
}
/**
 * Returns an empty {@code Optional} instance.  No value is present for this
 * Optional.
 *
 * @apiNote Though it may be tempting to do so, avoid testing if an object
 * is empty by comparing with {@code ==} against instances returned by
 * {@code Option.empty()}. There is no guarantee that it is a singleton.
 * Instead, use {@link #isPresent()}.
 *
 * @param <T> Type of the non-existent value
 * @return an empty {@code Optional}
 */
public static<T> Optional<T> empty() {
	@SuppressWarnings("unchecked")
	Optional<T> t = (Optional<T>) EMPTY;
	return t;
}
/**
 * Returns an {@code Optional} with the specified present non-null value.
 *
 * @param <T> the class of the value
 * @param value the value to be present, which must be non-null
 * @return an {@code Optional} with the value present
 * @throws NullPointerException if value is null
 */
public static <T> Optional<T> of(T value) {
	return new Optional<>(value);
}

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版权声明：本文为CSDN博主「程序小白-M」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/zym_1321/article/details/107769743