Objects.equals() / Objects.toString() / Objects.requireNonNull()

// Performs a null-safe equality comparison.
boolean result = Objects.equals(Object a, Object b);

// Converts an object to a string, safely handling null.
String str = Objects.toString(Object o);
String str = Objects.toString(Object o, String nullDefault);

// Throws NullPointerException if the argument is null.
T value = Objects.requireNonNull(T obj);
T value = Objects.requireNonNull(T obj, String message);

// Checks whether a value is null or non-null.
boolean isNull   = Objects.isNull(Object obj);
boolean nonNull  = Objects.nonNull(Object obj);

// Computes a null-safe hash code.
int hash = Objects.hashCode(Object o);
int hash = Objects.hash(Object... values);

import java.util.Objects;

// Use equals() to compare values safely with null.
String a = null;
String b = "Hello";
System.out.println(Objects.equals(a, b));    // Prints "false".
System.out.println(Objects.equals(a, null)); // Prints "true".
// a.equals(b) would throw NullPointerException, but Objects.equals() is safe.

// Use toString() to convert null to a string.
String name = null;
System.out.println(Objects.toString(name));              // Prints "null".
System.out.println(Objects.toString(name, "Anonymous")); // Prints "Anonymous".

// Use requireNonNull() to validate arguments.
class User {
    private String name;

    User(String name) {
        this.name = Objects.requireNonNull(name, "name must not be null.");
    }
}

try {
    User u = new User(null); // Throws NullPointerException.
} catch (NullPointerException e) {
    System.out.println(e.getMessage()); // Prints "name must not be null.".
}

// Use hash() to implement hashCode.
class Point {
    int x, y;
    Point(int x, int y) { this.x = x; this.y = y; }

    @Override
    public int hashCode() {
        return Objects.hash(x, y); // Computes a hash code from multiple fields concisely.
    }
}

Objects.equals() is commonly used in equals() implementations because it handles null safely. The standard a.equals(b) throws a NullPointerException when a is null, but Objects.equals(a, b) handles that case safely.

requireNonNull() is used to validate arguments in constructors and public methods, allowing you to detect errors early at the point where null should never appear. Since Java 9, you can also use Objects.requireNonNullElse(obj, defaultValue) to provide a default value when null is passed.

For type checking, see getClass() / instanceof.