此检查建议用对象/流静态方法替换空检查
例如：
Bmb bmb = bmbRepository.findById(allByUserId.getBmId()).orElseThrow(); if (bmb != null) { it.setBmb(bmb); } else { it.setBmb(new Bmb()); }
提示说用Objects.requireNonNullElseGet,我用Objects.requireNonNullElse也行
Objects.requireNonNullElse如果第一个对象为空，则返回第二个对象，第二个对象为空也会抛出空指针异常。
还有其他对象判空的静态方法也比较好用，而且减少代码量。
建议使用Objects.requireNonNull(T obj)，该方法主要用于提早判断对象是否为空，以便更早的抛出空指针异常。
自己可以进去看源码。
对象静态方法目录：
1、public static boolean equals(Object a, Object b)
2、public static boolean deepEquals(Object a, Object b)
3、public static int hashCode(Object o)
4、public static int hash(Object... values)
5、public static String toString(Object o)
6、public static String toString(Object o, String nullDefault)
7、public static <T> int compare(T a, T b, Comparator<? super T> c)
8、public static <T> T requireNonNull(T obj)
9、public static <T> T requireNonNull(T obj, String message)
10、public static boolean isNull(Object obj)
11、public static boolean nonNull(Object obj)
12、public static <T> T requireNonNullElse(T obj, T defaultObj)
13、public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier)
14、public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier)
15、public static int checkIndex(int index, int length)
16、public static int checkFromToIndex(int fromIndex, int toIndex, int length)
17、public static int checkFromIndexSize(int fromIndex, int size, int length)
对象的静态方法及源码注释：
1、public static boolean equals(Object a, Object b) 返回方法目录
/** * Returns {@code true} if the arguments are equal to each other * and {@code false} otherwise. * Consequently, if both arguments are {@code null}, {@code true} * is returned. Otherwise, if the first argument is not {@code * null}, equality is determined by calling the {@link * Object#equals equals} method of the first argument with the * second argument of this method. Otherwise, {@code false} is * returned. * * @param a an object * @param b an object to be compared with {@code a} for equality * @return {@code true} if the arguments are equal to each other * and {@code false} otherwise * @see Object#equals(Object) */ public static boolean equals(Object a, Object b) { return (a == b) || (a != null && a.equals(b)); }
2、public static boolean deepEquals(Object a, Object b) 返回方法目录
/** * Returns {@code true} if the arguments are deeply equal to each other * and {@code false} otherwise. * * Two {@code null} values are deeply equal. If both arguments are * arrays, the algorithm in {@link Arrays#deepEquals(Object[], * Object[]) Arrays.deepEquals} is used to determine equality. * Otherwise, equality is determined by using the {@link * Object#equals equals} method of the first argument. * * @param a an object * @param b an object to be compared with {@code a} for deep equality * @return {@code true} if the arguments are deeply equal to each other * and {@code false} otherwise * @see Arrays#deepEquals(Object[], Object[]) * @see Objects#equals(Object, Object) */ public static boolean deepEquals(Object a, Object b) { if (a == b) return true; else if (a == null || b == null) return false; else return Arrays.deepEquals0(a, b); }
3、public static int hashCode(Object o) 返回方法目录
/** * Returns the hash code of a non-{@code null} argument and 0 for * a {@code null} argument. * * @param o an object * @return the hash code of a non-{@code null} argument and 0 for * a {@code null} argument * @see Object#hashCode */ public static int hashCode(Object o) { return o != null ? o.hashCode() : 0; }
4、public static int hash(Object... values) 返回方法目录
/** * Generates a hash code for a sequence of input values. The hash * code is generated as if all the input values were placed into an * array, and that array were hashed by calling {@link * Arrays#hashCode(Object[])}. * * <p>This method is useful for implementing {@link * Object#hashCode()} on objects containing multiple fields. For * example, if an object that has three fields, {@code x}, {@code * y}, and {@code z}, one could write: * * <blockquote><pre> * @Override public int hashCode() { * return Objects.hash(x, y, z); * } * </pre></blockquote> * * <b>Warning: When a single object reference is supplied, the returned * value does not equal the hash code of that object reference.</b> This * value can be computed by calling {@link #hashCode(Object)}. * * @param values the values to be hashed * @return a hash value of the sequence of input values * @see Arrays#hashCode(Object[]) * @see List#hashCode */ public static int hash(Object... values) { return Arrays.hashCode(values); }
5、public static String toString(Object o) 返回方法目录
/** * Returns the result of calling {@code toString} for a non-{@code * null} argument and {@code "null"} for a {@code null} argument. * * @param o an object * @return the result of calling {@code toString} for a non-{@code * null} argument and {@code "null"} for a {@code null} argument * @see Object#toString * @see String#valueOf(Object) */ public static String toString(Object o) { return String.valueOf(o); }
6、public static String toString(Object o, String nullDefault) 返回方法目录
/** * Returns the result of calling {@code toString} on the first * argument if the first argument is not {@code null} and returns * the second argument otherwise. * * @param o an object * @param nullDefault string to return if the first argument is * {@code null} * @return the result of calling {@code toString} on the first * argument if it is not {@code null} and the second argument * otherwise. * @see Objects#toString(Object) */ public static String toString(Object o, String nullDefault) { return (o != null) ? o.toString() : nullDefault; }
7、public static <T> int compare(T a, T b, Comparator<? super T> c) 返回方法目录
/** * Returns 0 if the arguments are identical and {@code * c.compare(a, b)} otherwise. * Consequently, if both arguments are {@code null} 0 * is returned. * * <p>Note that if one of the arguments is {@code null}, a {@code * NullPointerException} may or may not be thrown depending on * what ordering policy, if any, the {@link Comparator Comparator} * chooses to have for {@code null} values. * * @param <T> the type of the objects being compared * @param a an object * @param b an object to be compared with {@code a} * @param c the {@code Comparator} to compare the first two arguments * @return 0 if the arguments are identical and {@code * c.compare(a, b)} otherwise. * @see Comparable * @see Comparator */ public static <T> int compare(T a, T b, Comparator<? super T> c) { return (a == b) ? 0 : c.compare(a, b); }
8、public static <T> T requireNonNull(T obj) 返回方法目录
/** * 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(); return obj; }
解释：检查定义的对象引用不为空。设计该方法主要用来做方法和构造函数中的参数校验
如上，如果直接使用仍然是抛出一个NPE，除了能提早检测和抛出异常，无法直接在业务中使用
9、public static <T> T requireNonNull(T obj, String message) 返回方法目录
/** * Checks that the specified object reference is not {@code null} and * throws a customized {@link NullPointerException} if it is. This method * is designed primarily for doing parameter validation in methods and * constructors with multiple parameters, as demonstrated below: * <blockquote><pre> * public Foo(Bar bar, Baz baz) { * this.bar = Objects.requireNonNull(bar, "bar must not be null"); * this.baz = Objects.requireNonNull(baz, "baz must not be null"); * } * </pre></blockquote> * * @param obj the object reference to check for nullity * @param message detail message to be used in the event that a {@code * NullPointerException} is thrown * @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, String message) { if (obj == null) throw new NullPointerException(message); return obj; }
解释：相比上一个方法，这个方法可以自定义报错信息，message是要报错的信息。
10、public static boolean isNull(Object obj) 返回方法目录
/** * Returns {@code true} if the provided reference is {@code null} otherwise * returns {@code false}. * * @apiNote This method exists to be used as a * {@link java.util.function.Predicate}, {@code filter(Objects::isNull)} * * @param obj a reference to be checked against {@code null} * @return {@code true} if the provided reference is {@code null} otherwise * {@code false} * * @see java.util.function.Predicate * @since 1.8 */ public static boolean isNull(Object obj) { return obj == null; }
11、public static boolean nonNull(Object obj) 返回方法目录
/** * Returns {@code true} if the provided reference is non-{@code null} * otherwise returns {@code false}. * * @apiNote This method exists to be used as a * {@link java.util.function.Predicate}, {@code filter(Objects::nonNull)} * * @param obj a reference to be checked against {@code null} * @return {@code true} if the provided reference is non-{@code null} * otherwise {@code false} * * @see java.util.function.Predicate * @since 1.8 */ public static boolean nonNull(Object obj) { return obj != null; }
12、public static <T> T requireNonNullElse(T obj, T defaultObj) 返回方法目录
/** * Returns the first argument if it is non-{@code null} and * otherwise returns the non-{@code null} second argument. * * @param obj an object * @param defaultObj a non-{@code null} object to return if the first argument * is {@code null} * @param <T> the type of the reference * @return the first argument if it is non-{@code null} and * otherwise the second argument if it is non-{@code null} * @throws NullPointerException if both {@code obj} is null and * {@code defaultObj} is {@code null} * @since 9 */ public static <T> T requireNonNullElse(T obj, T defaultObj) { return (obj != null) ? obj : requireNonNull(defaultObj, "defaultObj"); }
13、public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier) 返回方法目录
/** * Returns the first argument if it is non-{@code null} and otherwise * returns the non-{@code null} value of {@code supplier.get()}. * * @param obj an object * @param supplier of a non-{@code null} object to return if the first argument * is {@code null} * @param <T> the type of the first argument and return type * @return the first argument if it is non-{@code null} and otherwise * the value from {@code supplier.get()} if it is non-{@code null} * @throws NullPointerException if both {@code obj} is null and * either the {@code supplier} is {@code null} or * the {@code supplier.get()} value is {@code null} * @since 9 */ public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier) { return (obj != null) ? obj : requireNonNull(requireNonNull(supplier, "supplier").get(), "supplier.get()"); }
14、public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) 返回方法目录
/** * Checks that the specified object reference is not {@code null} and * throws a customized {@link NullPointerException} if it is. * * <p>Unlike the method {@link #requireNonNull(Object, String)}, * this method allows creation of the message to be deferred until * after the null check is made. While this may confer a * performance advantage in the non-null case, when deciding to * call this method care should be taken that the costs of * creating the message supplier are less than the cost of just * creating the string message directly. * * @param obj the object reference to check for nullity * @param messageSupplier supplier of the detail message to be * used in the event that a {@code NullPointerException} is thrown * @param <T> the type of the reference * @return {@code obj} if not {@code null} * @throws NullPointerException if {@code obj} is {@code null} * @since 1.8 */ public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) { if (obj == null) throw new NullPointerException(messageSupplier == null ? null : messageSupplier.get()); return obj; }
15、public static int checkIndex(int index, int length) 返回方法目录
/** * Checks if the {@code index} is within the bounds of the range from * {@code 0} (inclusive) to {@code length} (exclusive). * * <p>The {@code index} is defined to be out of bounds if any of the * following inequalities is true: * <ul> * <li>{@code index < 0}</li> * <li>{@code index >= length}</li> * <li>{@code length < 0}, which is implied from the former inequalities</li> * </ul> * * @param index the index * @param length the upper-bound (exclusive) of the range * @return {@code index} if it is within bounds of the range * @throws IndexOutOfBoundsException if the {@code index} is out of bounds * @since 9 */ @ForceInline public static int checkIndex(int index, int length) { return Preconditions.checkIndex(index, length, null); }
16、public static int checkFromToIndex(int fromIndex, int toIndex, int length) 返回方法目录
/** * Checks if the sub-range from {@code fromIndex} (inclusive) to * {@code toIndex} (exclusive) is within the bounds of range from {@code 0} * (inclusive) to {@code length} (exclusive). * * <p>The sub-range is defined to be out of bounds if any of the following * inequalities is true: * <ul> * <li>{@code fromIndex < 0}</li> * <li>{@code fromIndex > toIndex}</li> * <li>{@code toIndex > length}</li> * <li>{@code length < 0}, which is implied from the former inequalities</li> * </ul> * * @param fromIndex the lower-bound (inclusive) of the sub-range * @param toIndex the upper-bound (exclusive) of the sub-range * @param length the upper-bound (exclusive) the range * @return {@code fromIndex} if the sub-range within bounds of the range * @throws IndexOutOfBoundsException if the sub-range is out of bounds * @since 9 */ public static int checkFromToIndex(int fromIndex, int toIndex, int length) { return Preconditions.checkFromToIndex(fromIndex, toIndex, length, null); }
17、public static int checkFromIndexSize(int fromIndex, int size, int length) 返回方法目录
/** * Checks if the sub-range from {@code fromIndex} (inclusive) to * {@code fromIndex + size} (exclusive) is within the bounds of range from * {@code 0} (inclusive) to {@code length} (exclusive). * * <p>The sub-range is defined to be out of bounds if any of the following * inequalities is true: * <ul> * <li>{@code fromIndex < 0}</li> * <li>{@code size < 0}</li> * <li>{@code fromIndex + size > length}, taking into account integer overflow</li> * <li>{@code length < 0}, which is implied from the former inequalities</li> * </ul> * * @param fromIndex the lower-bound (inclusive) of the sub-interval * @param size the size of the sub-range * @param length the upper-bound (exclusive) of the range * @return {@code fromIndex} if the sub-range within bounds of the range * @throws IndexOutOfBoundsException if the sub-range is out of bounds * @since 9 */ public static int checkFromIndexSize(int fromIndex, int size, int length) { return Preconditions.checkFromIndexSize(fromIndex, size, length, null); }