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Object

java.lang

Class Object

  • java.lang.Object


  • public class Object
    The root class of the Java class hierarchy. All non-primitive types (including arrays) inherit either directly or indirectly from this class.

    Object provides some fundamental methods for accessing the Class of an object, getting its hashCode(), or checking whether one object equals(Object) another. The toString() method can be used to convert an object reference into a printable string and is often overridden in subclasses.

    The #wait() and #notify() methods provide a foundation for synchronization, acquiring and releasing an internal monitor associated with each Object.

    • Constructor Summary

      Constructors
      Constructor and Description
      Object()
      Constructs a new instance of Object.
    • Method Summary

      Methods
      Modifier and Type Method and Description
      boolean equals(Object o)
      Compares this instance with the specified object and indicates if they are equal.
      Class<? extends Object> getClass()
      Returns the unique instance of Class which represents this object's class.
      int hashCode()
      Returns an integer hash code for this object.
      String toString()
      Returns a string containing a concise, human-readable description of this object.
    • Constructor Detail

      • Object

        public Object()
        Constructs a new instance of Object.
    • Method Detail

      • equals

        public boolean equals(Object o)
        Compares this instance with the specified object and indicates if they are equal. In order to be equal, o must represent the same object as this instance using a class-specific comparison. The general contract is that this comparison should be both transitive and reflexive.

        The implementation in Object returns true only if o is the exact same object as the receiver (using the == operator for comparison). Subclasses often implement equals(Object) so that it takes into account the two object's types and states.

        The general contract for the equals(Object) and hashCode() methods is that if equals returns true for any two objects, then hashCode() must return the same value for these objects. This means that subclasses of Object usually override either both methods or none of them.

        Parameters:
        o - the object to compare this instance with.
        Returns:
        true if the specified object is equal to this Object; false otherwise.
        See Also:
        hashCode()
      • getClass

        public final Class<? extends Object> getClass()
        Returns the unique instance of Class which represents this object's class. Note that getClass() is a special case in that it actually returns Class<? extends Foo> where Foo is the erasure of the type of expression getClass() was called upon.

        As an example, the following code actually compiles, although one might think it shouldn't:

         List l = new ArrayList();
         Class extends List> c = l.getClass();
         
        Returns:
        this object's Class instance.
      • hashCode

        public int hashCode()
        Returns an integer hash code for this object. By contract, any two objects for which equals(Object) returns true must return the same hash code value. This means that subclasses of Object usually override both methods or neither method.
        Returns:
        this object's hash code.
        See Also:
        equals(java.lang.Object)
      • toString

        public String toString()
        Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation simply concatenates the class name, the '@' sign and a hexadecimal representation of the object's hashCode(), that is, it is equivalent to the following expression:
         getClass().getName() + '@' + Integer.toHexString(hashCode())
         
        Returns:
        a printable representation of this object.