Java Strings - using Strings in practice
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The document provides a comprehensive overview of Java Strings, covering their nature as immutable character sequences and ways to instantiate them using literals or constructors. It discusses memory management related to strings, including string interning and the string pool. Additionally, it covers string formatting, manipulation, use cases, and references for further reading.
Java Strings - using Strings in practice
- 1. Java Strings Using Strings in practice
- 2. Java String • Character sequence • Immutable • Class defined in the java.lang package • Instantiate a String Object: • Using a String literal (series of characters enclosed in double quotes) String s1 = “Cat”; • Via the String constructor (see API for different constructors) String s2 = new String(“Cat”);
- 3. Java String – Memory • Output of the following code?
- 4. Java String – Memory • Output of the following code? s1 == s2 :true s1 == s3 :false
- 5. Java String – Memory • Java Memory Heap as a Java Object String s2 = new String(“Cat”); • String pool in the Java Memory Heap • String interning • Flyweight pattern String s1 = “Cat”;
- 6. Java String – API • Extends java.lang.Object • E.g.: equals(other: Object) : boolean, hashCode() : int, … • Implements: Serializable, CharSequence, Comparable<String> • E.g.: compareTo(other: String) : int, charAt(index: int) : char, … • String specific API • E.g.: isEmpty() : boolean, …
- 8. StringBuffer • Mutable • Thread-safe • Slower
- 9. Java String – Formatting • String.format • Conversion specifiers: %d (decimal integer), %f (floating point), %c (any character), … • Many more options (see documentation) String fs; fs = String.format("Variable 1 (%f) is of type float, while " + "the 2nd variable (%d) is an integer, " + "and the 3rd one, %s, is a string...", floatVar, intVar, stringVar); • Formatter class (java.util) StringBuilder sbuf = new StringBuilder(); Formatter fmt = new Formatter(sbuf); fmt.format("PI = %f%n", Math.PI); System.out.print(sbuf.toString()); // you can continue to append data to sbuf here.
- 10. Use cases • String instantiation • String concatenation • String duplication • String manipulation • … => Questions: • Performance? • Thread-safe? • …
- 11. Use cases – Instantiation • Benchmarking: • String Object: new (with various constructors), literal • StringBuffer constructor(s) • StringBuilder constructor(s)
- 12. Use cases – Concatenation • Benchmarking: • String Object: Operator +, concat method • StringBuffer append • StringBuilder append • …
- 13. Conclusion • Creating Java String objects • Concatenating strings
- 15. References • Java String • https://docs.oracle.com/javase/tutorial/java/data/strings.html • Java String – Memory: • https://www.journaldev.com/797/what-is-java-string-pool • https://en.wikipedia.org/wiki/String_interning • https://en.wikipedia.org/wiki/Flyweight_pattern • https://www.javatpoint.com/how-to-optimize-java-string-creation • Java String – API • https://docs.oracle.com/javase/8/docs/api/java/lang/String.html
- 16. References • Java String - Formatting • https://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html • https://dzone.com/articles/java-string-format-examples • StringBuilder • StringBuffer
Editor's Notes
- #3: https://www.journaldev.com/1321/java-string-interview-questions-and-answers#java-string https://docs.oracle.com/javase/tutorial/java/data/strings.html
- #6: When we create a String using double quotes, JVM looks in the String pool to find if any other String is stored with the same value. If found, it just returns the reference to that String object else it creates a new String object with given value and stores it in the String pool. When we use the new operator, JVM creates the String object but don’t store it into the String Pool. We can use intern() method to store the String object into String pool or return the reference if there is already a String with equal value present in the pool.
- #7: https://docs.oracle.com/javase/8/docs/api/java/lang/String.html char : charAt(int index) Returns the char value at the specified index. String : concat(String str) Concatenates the specified string to the end of this string. boolean : contains(CharSequence s) Returns true if and only if this string contains the specified sequence of char values. int : indexOf(String str) Returns the index within this string of the first occurrence of the specified substring. String : intern() Returns a canonical representation for the string object. Boolean : isEmpty() Returns true if, and only if, length() is 0. …
- #9: The string is immutable and final in Java, so whenever we do String manipulation, it creates a new String. String manipulations are resource consuming, so java provides two utility classes for String manipulations – StringBuffer and StringBuilder. StringBuffer and StringBuilder are mutable classes. StringBuffer operations are thread-safe and synchronized where StringBuilder operations are not thread-safe. So in a multi-threaded environment, we should use StringBuffer but in the single-threaded environment, we should use StringBuilder. StringBuilder performance is fast than StringBuffer because of no overhead of synchronization.