Are strings garbage collected?

Are locally created Java arrays (inside for or while loop) garbage collected automatically or does it result in memory leaks?

• Consider the following code: [code] int testCases = readInt(); // This array stores precomputed prime numbers in range [m, n] boolean[] primes = null; int m = 0; int n = 0; for(int t=0; t<testCases; t++) { m = readInt(); n = readInt(); // primes array will be created testCases times primes = new boolean[n-m+1]; // Do I need to uncomment following statement or primes array will be garbage collected automatically? // primes = null; } [/code] How can I ensure that above code won't result in memory leaks for larger values of testCases?

• Answer:

  They will be garbage collected since there is no external reference to them. Java, and most other languages that manage memory automatically, use a link count or reference count to determine when memory can be freed. Every  time you assign the address of a variable or allocation the reference count is incremented. When that variable goes out of scope, the refernece count is decremented. When the garbage collection routine runs, all memory allocations with a reference count of 0 can be safely freed. All memory associated with the arrays created inside the loop will have a reference count of at least one because they are scoped to the loop. If you assign elements of that array to other loop scoped variables the refence count will go up but those variables are also scoped to the array so when they fall out of scope the reference count will be decremented. As soon as the loop finishes everything created within it falls out of scope, the final counts will go to zero. The next call of the garbage collection routine will mark the memory as free.