使用Optional.of、ofNullable、orElse、orElseGet遇到的坑

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已于 2022-09-03 22:57:01 修改 · 1.4w 阅读

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于 2021-06-10 12:38:48 首次发布

本文详细解析了Java中Optional类的of()与ofNullable()方法的区别，以及orElse()与orElseGet()方法的不同之处。通过源码分析及实例演示，帮助读者更好地理解和应用这些方法。

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of()与ofNullable()的区别

从方法名上对比理解，就是ofNullable() 可以支持null值，那of()就不支持null值。

下面看下源码：

java.util.Optional.java

    /**
     * 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);
    }

    /**
     * Constructs an instance with the value present.
     *
     * @param value the non-null value to be present
     * @throws NullPointerException if value is null
     */
    private Optional(T value) {
   
   
        this.value = Objects.requireNonNull(value);
    }

java.util.Objects.java

    /**
     * Checks that the specified object reference is not {@code null}. This
     * method is designed primarily for doing parameter validation in methods
     * and constructors, as demonstrated below:
     * <blockquote><pre>
     * public Foo(Bar bar) {
     *     this.bar = Objects.requireNonNull(bar);
     * }
     * </pre></blockquote>
     *
     * @param obj the object reference to check for nullity
     * @param <T> the type of the reference
     * @return {@code obj} if not {@code null}
     * @throws NullPointerException if {@code obj} is {@code null}
     */
    public static <T> T requireNonNull(T obj) {
   
   
        if (obj == null)
            throw new NullPointerException(