Java Strings - using Strings in practice

Jul 11, 2024Download as pptx, pdf

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Joris Schelfaut

Short overview of how String objects can be used in Java

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”);

Java String – Memory
• Output of the following code?

Java String – Memory
• Output of the following code?
s1 == s2 :true
s1 == s3 :false

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”;

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, …

StringBuffer
• Mutable
• Thread-safe
• Slower

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.

Use cases
• String instantiation
• String concatenation
• String duplication
• String manipulation
• …
=> Questions:
• Performance?
• Thread-safe?
• …

Use cases – Instantiation
• Benchmarking:
• String Object: new (with various constructors), literal
• StringBuffer constructor(s)
• StringBuilder constructor(s)

Use cases – Concatenation
• Benchmarking:
• String Object: Operator +, concat method
• StringBuffer append
• StringBuilder append
• …

Conclusion
• Creating Java String objects
• Concatenating strings

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

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

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