pointer : Java Glossary

You may have heard some FUDster claiming that Java sucks roadkill because it has no pointers. He jeers, How can you write serious code without pointers? In Java are you actually limited to FØRTRAN style problems: no linked lists, no queues etc? Java does not have raw pointers like C or C++. It has something almost as powerful, but many times safer called references (Java refers to them as pointers in one place, the NullPointerException). They are like pointers, except that the dangerous features are removed, namely:

• pointer arithmetic.
• random initialisation values from failure to initialise.
• dangling pointers to deleted Objects. Java has garbage collection — automatic detection and deletion of Objects no longer is use.
• mismatched types and unions.
• You can’t construct references out of thin air, only with new.
• Unlike pointers, references cannot point into the middle of an Object.
• References are null or always point to something valid of the type they claim to.
• Pointers always point directly to data. References are usually implemented as handles, not pointers. A handle is a pointer to a pointer. This allows Objects to be moved around to compact fragmented RAM (Random Access Memory) without having to find and adjust all the pointers to those Objects.
• In C++ you explicitly reference and dereference the layers of pointer indirection to get at the data or to more direct pointers using a subtle interplay of &, *, -> and . operators. This gets quite convoluted. In Java you rarely think about defreferencing. Java automatically dereferences as needed helped along with the uniform referencing/defreferencing . operator where there is more that one level of indirection. For primitives and direct references to Objects, there is no need for an operator of any kind.

• Every downcast has to be checked at run time to ensure the Object truly is of the type your cast claims it to be.
• Nearly every time you put an Object into an array, the runtime must check the type to be sure it is compatible with the allocated type of the array, (which is distinct from the declared type of the array reference.)
• Implementations of linked structures typically require extra tiny glue Objects that point to the Objects linked. With raw pointers, typically you manage to embed these pointers directly into your Objects.

So they decided to rename them references. But old habits die hard and people, even those at Sun, sometimes continued to call them pointers. The further wanted a new term that allowed for the many ways you can implement Java pointers e.g. via machine virtual RAM pointers, segmented pointers, 64-bit addressing pointers or handles. The word pointer leaked through in various places including NullPointerException.

No More Pointers?

Most studies agree that pointers are one of the primary features that enable programmers to inject bugs into their code. Given that structures are gone and arrays and strings are objects, the need for pointers to these constructs goes away. Thus, Java has no pointer data types. Any task that would require arrays, structures and pointers in C can be more easily and reliably performed by declaring objects and arrays of objects. Instead of complex pointer manipulation on array pointers, you access arrays by their arithmetic indices. The Java run-time system checks all array indexing to ensure indices are within the bounds of the array.

You no longer have dangling pointers and trashing of memory because of incorrect pointers because there are no pointers in Java.
~ James Gosling (1955-05-18 age:62), co-inventor of Java, in a paper The Java Language Environment co-authored with Henry McGilton

An object is a class instance or an array.
The reference values (often just references) are pointers to these objects and a special null reference, which refers to no object.
~ James Gosling (1955-05-18 age:62), co-inventor of Java,

JLS (Java Language Specification): definition of Object