string-interning

问题 I have a large dataset from an analytics provider. It arrives in JSON and I parse it into a hash, but due to the size of the set I'm ballooning to over a gig in memory usage. Almost everything starts as strings (a few values are numerical), and while of course the keys are duplicated many times, many of the values are repeated as well. So I was thinking, why not symbolize all the (non-numerical) values, as well? I've found some discusion of potential problems, but I figure it would be nice to

问题 Consider: String s1 = new StringBuilder("Cattie").append(" & Doggie").toString(); System.out.println(s1.intern() == s1); // true why? System.out.println(s1 == "Cattie & Doggie"); // true another why? String s2 = new StringBuilder("ja").append("va").toString(); System.out.println(s2.intern() == s2); // false String s3 = new String("Cattie & Doggie"); System.out.println(s3.intern() == s3); // false System.out.println(s3 == "Cattie & Doggie"); // false I got confused why they are resulting

问题 Consider: String s1 = new StringBuilder("Cattie").append(" & Doggie").toString(); System.out.println(s1.intern() == s1); // true why? System.out.println(s1 == "Cattie & Doggie"); // true another why? String s2 = new StringBuilder("ja").append("va").toString(); System.out.println(s2.intern() == s2); // false String s3 = new String("Cattie & Doggie"); System.out.println(s3.intern() == s3); // false System.out.println(s3 == "Cattie & Doggie"); // false I got confused why they are resulting

问题 I recall seeing a couple of string-intensive programs that do a lot of string comparison but relatively few string manipulation, and that have used a separate table to map strings to identifiers for efficient equality and lower memory footprint, e.g.: public class Name { public static Map<String, Name> names = new SomeMap<String, Name>(); public static Name from(String s) { Name n = names.get(s); if (n == null) { n = new Name(s); names.put(s, n); } return n; } private final String str;

问题 I recall seeing a couple of string-intensive programs that do a lot of string comparison but relatively few string manipulation, and that have used a separate table to map strings to identifiers for efficient equality and lower memory footprint, e.g.: public class Name { public static Map<String, Name> names = new SomeMap<String, Name>(); public static Name from(String s) { Name n = names.get(s); if (n == null) { n = new Name(s); names.put(s, n); } return n; } private final String str;

问题 I recall seeing a couple of string-intensive programs that do a lot of string comparison but relatively few string manipulation, and that have used a separate table to map strings to identifiers for efficient equality and lower memory footprint, e.g.: public class Name { public static Map<String, Name> names = new SomeMap<String, Name>(); public static Name from(String s) { Name n = names.get(s); if (n == null) { n = new Name(s); names.put(s, n); } return n; } private final String str;

问题 Let's say I have a class as follows: class Apple { String apple; Apple(String apple) { this.apple = apple; } } What makes the following code true? public boolean result() { Apple a = new Apple("apple"); Apple b = new Apple("apple"); return a.apple == b.apple; } Does Java automatically intern Strings set within instances of my objects? Is the only time that Java doesn't intern Strings is when they're created using new String("...") ? EDIT : Thanks for the answers, an extension to this question

问题 If I have a HashMap that looks like this: HashMap<String, MyObject> where the String key is a field in MyObject , does this string value get stored twice? So when I add entries: _myMap.put(myObj.getName(), myObj); Am I using double the String size in terms of memory? Or does Java do something clever behind the scenes? Thanks 回答1: Java uses the reference, so it is just a pointer to the string that it stores twice. So you don't have to worry if your string is huge, it will still be the same

问题 Is there something like intern() method in C or C++ like there is in Java ? If there isn't, how can I carry out string interning in C or C++? 回答1: boost::flyweight< std::string > seems to be exactly what you're looking for. 回答2: Is there something like intern() method in C like we have in Java ? Not in the standard C library. If there isn't, how to carry out string interning in C? With great difficulty, I fear. The first problem is that "string" is not a well-defined thing in C. Instead you

问题 Is there something like intern() method in C or C++ like there is in Java ? If there isn't, how can I carry out string interning in C or C++? 回答1: boost::flyweight< std::string > seems to be exactly what you're looking for. 回答2: Is there something like intern() method in C like we have in Java ? Not in the standard C library. If there isn't, how to carry out string interning in C? With great difficulty, I fear. The first problem is that "string" is not a well-defined thing in C. Instead you