Java : Objects with Examples

Objects (Java SE 18 & JDK 18) API Examples.
You will find code examples on most Objects methods.

Summary

This class consists of static utility methods for operating on objects, or checking certain conditions before operation.

Class diagram

final String str1 = null;
final String str2 = "abcd";

System.out.println(Objects.equals(str1, str2)); // false
System.out.println(Objects.equals(str1, null)); // true
System.out.println(Objects.equals(str2, "abcd")); // true

System.out.println(Objects.hash(123, 789, "abc")); // 268807

final var list = new ArrayList<String>();
list.add("a");
list.add(null);
list.add("b");
list.add(null);
list.add("c");

System.out.println(list); // [a, null, b, null, c]

final var result = list.stream().filter(Objects::nonNull).toList();
System.out.println(result); // [a, b, c]

Methods

static int checkFromIndexSize (int fromIndex, int size, int length)

Checks if the sub-range from fromIndex (inclusive) to fromIndex + size (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).

System.out.println(Objects.checkFromIndexSize(0, 0, 5)); // 0
System.out.println(Objects.checkFromIndexSize(0, 1, 5)); // 0
System.out.println(Objects.checkFromIndexSize(0, 2, 5)); // 0
System.out.println(Objects.checkFromIndexSize(0, 3, 5)); // 0
System.out.println(Objects.checkFromIndexSize(0, 4, 5)); // 0
System.out.println(Objects.checkFromIndexSize(0, 5, 5)); // 0
//Objects.checkFromIndexSize(0, 6, 5); // IndexOutOfBoundsException

System.out.println(Objects.checkFromIndexSize(3, 0, 5)); // 3
System.out.println(Objects.checkFromIndexSize(3, 1, 5)); // 3
System.out.println(Objects.checkFromIndexSize(3, 2, 5)); // 3
//Objects.checkFromIndexSize(3, 3, 5); // IndexOutOfBoundsException

System.out.println(Objects.checkFromIndexSize(0, 1, 5)); // 0
System.out.println(Objects.checkFromIndexSize(1, 1, 5)); // 1
System.out.println(Objects.checkFromIndexSize(2, 1, 5)); // 2
System.out.println(Objects.checkFromIndexSize(3, 1, 5)); // 3
System.out.println(Objects.checkFromIndexSize(4, 1, 5)); // 4
//Objects.checkFromIndexSize(5, 1, 5); // IndexOutOfBoundsException

//Objects.checkFromIndexSize(-1, 0, 5); // IndexOutOfBoundsException
//Objects.checkFromIndexSize(0, -1, 5); // IndexOutOfBoundsException
//Objects.checkFromIndexSize(0, 0, -1); // IndexOutOfBoundsException

static long checkFromIndexSize (long fromIndex, long size, long length)

Checks if the sub-range from fromIndex (inclusive) to fromIndex + size (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).

Please see checkFromIndexSize(int fromIndex, int size, int length). This method is for a long type.

static int checkFromToIndex (int fromIndex, int toIndex, int length)

Checks if the sub-range from fromIndex (inclusive) to toIndex (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).

System.out.println(Objects.checkFromToIndex(0, 0, 5)); // 0
System.out.println(Objects.checkFromToIndex(0, 1, 5)); // 0
System.out.println(Objects.checkFromToIndex(0, 2, 5)); // 0
System.out.println(Objects.checkFromToIndex(0, 3, 5)); // 0
System.out.println(Objects.checkFromToIndex(0, 4, 5)); // 0
System.out.println(Objects.checkFromToIndex(0, 5, 5)); // 0
//Objects.checkFromToIndex(0, 6, 5); // IndexOutOfBoundsException

//Objects.checkFromToIndex(3, 2, 5); // IndexOutOfBoundsException
System.out.println(Objects.checkFromToIndex(3, 3, 5)); // 3
System.out.println(Objects.checkFromToIndex(3, 4, 5)); // 3
System.out.println(Objects.checkFromToIndex(3, 5, 5)); // 3
//Objects.checkFromToIndex(3, 6, 5); // IndexOutOfBoundsException

System.out.println(Objects.checkFromToIndex(0, 5, 5)); // 0
System.out.println(Objects.checkFromToIndex(1, 5, 5)); // 1
System.out.println(Objects.checkFromToIndex(2, 5, 5)); // 2
System.out.println(Objects.checkFromToIndex(3, 5, 5)); // 3
System.out.println(Objects.checkFromToIndex(4, 5, 5)); // 4
System.out.println(Objects.checkFromToIndex(5, 5, 5)); // 5
//Objects.checkFromToIndex(6, 5, 5); // IndexOutOfBoundsException

//Objects.checkFromToIndex(-1, 0, 5); // IndexOutOfBoundsException
//Objects.checkFromToIndex(0, -1, 5); // IndexOutOfBoundsException
//Objects.checkFromToIndex(0, 0, -1); // IndexOutOfBoundsException

static long checkFromToIndex (long fromIndex, long toIndex, long length)

Checks if the sub-range from fromIndex (inclusive) to toIndex (exclusive) is within the bounds of range from 0 (inclusive) to length (exclusive).

Please see checkFromToIndex(int fromIndex, int toIndex, int length). This method is for a long type.

static int checkIndex (int index, int length)

Checks if the index is within the bounds of the range from 0 (inclusive) to length (exclusive).

//Objects.checkIndex(-1, 5); // IndexOutOfBoundsException
System.out.println(Objects.checkIndex(0, 5)); // 0
System.out.println(Objects.checkIndex(1, 5)); // 1
System.out.println(Objects.checkIndex(2, 5)); // 2
System.out.println(Objects.checkIndex(3, 5)); // 3
System.out.println(Objects.checkIndex(4, 5)); // 4
//Objects.checkIndex(5, 5); // IndexOutOfBoundsException

//Objects.checkIndex(0, 0); // IndexOutOfBoundsException
//Objects.checkIndex(0, -1); // IndexOutOfBoundsException

static long checkIndex (long index, long length)

Checks if the index is within the bounds of the range from 0 (inclusive) to length (exclusive).

Please see checkIndex(int index, int length). This method is for a long type.

static <T> int compare (T a, T b, Comparator<? super T> c)

Returns 0 if the arguments are identical and c.compare(a, b) otherwise.

final var c = new Comparator<Integer>() {
    @Override
    public int compare(Integer o1, Integer o2) {
        if (o1 < o2) {
            return -1;
        } else if (o1 > o2) {
            return 1;
        } else {
            return 0;
        }
    }
};

System.out.println(Objects.compare(null, null, c)); // 0
System.out.println(Objects.compare(0, 5, c)); // -1
System.out.println(Objects.compare(5, 0, c)); // 1
System.out.println(Objects.compare(123, 123, c)); // 0

static boolean deepEquals (Object a, Object b)

Returns true if the arguments are deeply equal to each other and false otherwise.

final var str1 = "aaa";
final var str2 = "aaa";

System.out.println(Objects.equals(str1, str2)); // true
System.out.println(Objects.deepEquals(str1, str2)); // true

final var str3 = "bbb";

System.out.println(Objects.equals(str1, str3)); // false
System.out.println(Objects.deepEquals(str1, str3)); // false

final String[] array1 = {"a", "b", "c"};
final String[] array2 = {"a", "b", "c"};

System.out.println(Objects.equals(array1, array2)); // false
System.out.println(Objects.deepEquals(array1, array2)); // true

final String[] array3 = {"x", "y", "z"};

System.out.println(Objects.equals(array1, array3)); // false
System.out.println(Objects.deepEquals(array1, array3)); // false

final int[][] array1 = {
        {1, 2}, {3, 4},
        {5, 6}, {7, 8}
};
final int[][] array2 = {
        {1, 2}, {3, 4},
        {5, 6}, {7, 8}
};

System.out.println(Objects.equals(array1, array2)); // false
System.out.println(Objects.deepEquals(array1, array2)); // true

final int[][] array3 = {
        {1, 2}, {3, 4},
        {100, 200}, {300, 400}
};

System.out.println(Objects.equals(array1, array3)); // false
System.out.println(Objects.deepEquals(array1, array3)); // false

System.out.println(Objects.deepEquals(null, null)); // true
System.out.println(Objects.deepEquals(null, 1)); // false
System.out.println(Objects.deepEquals(2, null)); // false

static boolean equals (Object a, Object b)

Returns true if the arguments are equal to each other and false otherwise.

System.out.println(Objects.equals(1, 2)); // false
System.out.println(Objects.equals(3, 3)); // true
System.out.println(Objects.equals("abc", "def")); // false
System.out.println(Objects.equals("xxx", "xxx")); // true
System.out.println(Objects.equals("123", 123)); // false

System.out.println(Objects.equals(null, null)); // true
System.out.println(Objects.equals(null, 1)); // false
System.out.println(Objects.equals(2, null)); // false

final String[] array1 = {"a", "b", "c"};
final String[] array2 = {"a", "b", "c"};

System.out.println(Objects.equals(array1, array2)); // false
System.out.println(Objects.deepEquals(array1, array2)); // true

static int hash (Object... values)

Generates a hash code for a sequence of input values.

System.out.println(Objects.hash(1)); // 32
System.out.println(Objects.hash(1, 2)); // 994
System.out.println(Objects.hash(2, 1)); // 1024
System.out.println(Objects.hash(1, 2, 3)); // 30817
System.out.println(Objects.hash("a", "b", "c")); // 126145
System.out.println(Objects.hash(1, 2, 3, "a", "b", "c")); // 918165601

final int[] array1 = {1, 2, 3};
final int[] array2 = {1, 2, 3};
final int[] array3 = {4, 5, 6};
System.out.println(Objects.hash(array1)); // 1544785573
System.out.println(Objects.hash(array2)); // 664022656
System.out.println(Objects.hash(array3)); // 1426882641

System.out.println(Arrays.hashCode(array1)); // 30817
System.out.println(Arrays.hashCode(array2)); // 30817

static int hashCode (Object o)

Returns the hash code of a non-null argument and 0 for a null argument.

System.out.println(Objects.hashCode(null)); // 0
System.out.println(Objects.hashCode(123)); // 123
System.out.println(Objects.hashCode("abc")); // 96354

final int[] array1 = {1, 2, 3};
final int[] array2 = {1, 2, 3};
final int[] array3 = {4, 5, 6};
System.out.println(Objects.hashCode(array1)); // 1129405362
System.out.println(Objects.hashCode(array2)); // 556034497
System.out.println(Objects.hashCode(array3)); // 606135032

System.out.println(Arrays.hashCode(array1)); // 30817
System.out.println(Arrays.hashCode(array2)); // 30817

static boolean isNull (Object obj)

Returns true if the provided reference is null otherwise returns false.

System.out.println(Objects.isNull(null)); // true
System.out.println(Objects.isNull(123)); // false
System.out.println(Objects.isNull("abc")); // false

final var list = new ArrayList<String>();
list.add("a");
list.add(null);
list.add("b");
list.add(null);
list.add("c");

System.out.println(list); // [a, null, b, null, c]

final var result = list.stream().filter(Objects::isNull).toList();
System.out.println(result); // [null, null]

static boolean nonNull (Object obj)

Returns true if the provided reference is non-null otherwise returns false.

System.out.println(Objects.nonNull(null)); // false
System.out.println(Objects.nonNull(123)); // true
System.out.println(Objects.nonNull("abc")); // true

final var list = new ArrayList<String>();
list.add("a");
list.add(null);
list.add("b");
list.add(null);
list.add("c");

System.out.println(list); // [a, null, b, null, c]

final var result = list.stream().filter(Objects::nonNull).toList();
System.out.println(result); // [a, b, c]

static <T> T requireNonNull (T obj)

Checks that the specified object reference is not null.

class Book {
    private final String title;
    private final String content;

    Book(String title, String content) {
        this.title = Objects.requireNonNull(title);
        this.content = Objects.requireNonNull(content);
    }

    @Override
    public String toString() {
        return "title : " + title + ", content : " + content;
    }
}

//new Book(null, "abcd"); // NullPointerException
//new Book("XYZ", null); // NullPointerException

final var book = new Book("XYZ", "abcd");
System.out.println(book); // title : XYZ, content : abcd

static <T> T requireNonNull (T obj, String message)

Checks that the specified object reference is not null and throws a customized NullPointerException if it is.

class Book {
    private final String title;
    private final String content;

    Book(String title, String content) {
        this.title = Objects.requireNonNull(title, "title must not be null");
        this.content = Objects.requireNonNull(content, "content must not be null");
    }

    @Override
    public String toString() {
        return "title : " + title + ", content : " + content;
    }
}

//new Book(null, "abcd"); // NullPointerException: title must not be null
//new Book("XYZ", null); // NullPointerException: content must not be null

final var book = new Book("XYZ", "abcd");
System.out.println(book); // title : XYZ, content : abcd

static <T> T requireNonNull (T obj, Supplier<String> messageSupplier)

Checks that the specified object reference is not null and throws a customized NullPointerException if it is.

class Book {
    private final String title;
    private final String content;

    Book(String title, String content) {
        this.title = Objects.requireNonNull(title, () -> "title must not be null");
        this.content = Objects.requireNonNull(content, () -> "content must not be null");
    }

    @Override
    public String toString() {
        return "title : " + title + ", content : " + content;
    }
}

//new Book(null, "abcd"); // NullPointerException: title must not be null
//new Book("XYZ", null); // NullPointerException: content must not be null

final var book = new Book("XYZ", "abcd");
System.out.println(book); // title : XYZ, content : abcd

static <T> T requireNonNullElse (T obj, T defaultObj)

Returns the first argument if it is non-null and otherwise returns the non-null second argument.

class Book {
    private final String title;
    private final String content;

    Book(String title, String content) {
        this.title = Objects.requireNonNullElse(title, "default title");
        this.content = Objects.requireNonNullElse(content, "default content");
    }

    @Override
    public String toString() {
        return "title : " + title + ", content : " + content;
    }
}

final var book1 = new Book(null, "abcd");
System.out.println(book1); // title : default title, content : abcd

final var book2 = new Book("XYZ", null);
System.out.println(book2); // title : XYZ, content : default content

final var book3 = new Book("XYZ", "abcd");
System.out.println(book3); // title : XYZ, content : abcd

static <T> T requireNonNullElseGet (T obj, Supplier<? extends T> supplier)

Returns the first argument if it is non-null and otherwise returns the non-null value of supplier.get().

class Book {
    private final String title;
    private final String content;

    Book(String title, String content) {
        this.title = Objects.requireNonNullElseGet(title, () -> "default title");
        this.content = Objects.requireNonNullElseGet(content, () -> "default content");
    }

    @Override
    public String toString() {
        return "title : " + title + ", content : " + content;
    }
}

final var book1 = new Book(null, "abcd");
System.out.println(book1); // title : default title, content : abcd

final var book2 = new Book("XYZ", null);
System.out.println(book2); // title : XYZ, content : default content

final var book3 = new Book("XYZ", "abcd");
System.out.println(book3); // title : XYZ, content : abcd

static String toString (Object o)

Returns the result of calling toString for a non- null argument and "null" for a null argument.

final var str1 = Objects.toString(null);
System.out.println(str1); // "null"

final var str2 = Objects.toString(123);
System.out.println(str2); // "123"

final var str3 = Objects.toString("abcd");
System.out.println(str3); // "abcd"

static String toString (Object o, String nullDefault)

Returns the result of calling toString on the first argument if the first argument is not null and returns the second argument otherwise.

final var str1 = Objects.toString(null, "XYZ");
System.out.println(str1); // "XYZ"

final var str2 = Objects.toString(123, "XYZ");
System.out.println(str2); // "123"

final var str3 = Objects.toString("abcd", "XYZ");
System.out.println(str3); // "abcd"

API Examples
- Arrays
- Appendable
- AutoCloseable
- Boolean
- Class
- Cloneable
- Comparable
- Enum
- Iterable
- Object
- Readable
- Runtime
- Serializable
- StackWalker
- System

Java : Objects with Examples

Summary

Methods

static int checkFromIndexSize (int fromIndex, int size, int length)

static long checkFromIndexSize (long fromIndex, long size, long length)

static int checkFromToIndex (int fromIndex, int toIndex, int length)

static long checkFromToIndex (long fromIndex, long toIndex, long length)

static int checkIndex (int index, int length)

static long checkIndex (long index, long length)

static <T> int compare (T a, T b, Comparator<? super T> c)

static boolean deepEquals (Object a, Object b)

static boolean equals (Object a, Object b)

static int hash (Object... values)

static int hashCode (Object o)

static boolean isNull (Object obj)

static boolean nonNull (Object obj)

static <T> T requireNonNull (T obj)

static <T> T requireNonNull (T obj, String message)

static <T> T requireNonNull (T obj, Supplier<String> messageSupplier)

static <T> T requireNonNullElse (T obj, T defaultObj)

static <T> T requireNonNullElseGet (T obj, Supplier<? extends T> supplier)

static String toString (Object o)

static String toString (Object o, String nullDefault)

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