Strings

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WHY is a String?

String words = "apple is red"

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What is a String?

String words = "apple is red"

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Examples

String empty = new String();
String empty = "";

String oneCharacter = "a";

String word = "apple";

String phrase = "I'm sorry for what \"I said\" when I was hungry!";

String paragraph = "It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, we had everything before us, we had nothing before us, we were all going direct to Heaven, we were all going direct the other way – in short, the period was so far like the present period, that some of its noisiest authorities insisted on its being received, for good or for evil, in the superlative degree of comparison only.";

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new String({‘H’, ‘e’, ‘l’, ‘l’, ‘o’})

Constructor can take:

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Converting other data type to strings

String number = Integer.toString(55); // "55"
String number2 = String.valueOf(55); // "55"

String decimal = Double.toString(3.14); // "3.14"
String decimal2 = String.valueOf(3.14); // "3.14"

String character = Character.toString('c'); // "c"
String character2 = String.valueOf('c'); // "c"

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String Methods

.length()

String fruit = "apple is red";
fruit.length(); // 12

|a|p|p|l|e| |i|s| |r|e|d|

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String Methods

.length()

String empty = "";
empty.length(); // 0

String space = " ";
space.length(); // 1

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String Methods

.charAt(int index)

String fruit = "apple is red";

char firstCharacter =  fruit.charAt(0); // ‘a’
char sixthCharacter = fruit.charAt(5); // ‘ ’
char lastCharacter = fruit.charAt(fruit.length() - 1); // ‘d’
char secondToLastChar = fruit.charAt(fruit.length() - 2); // ‘e’

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String Methods

.substring(int beginIndex)

String fruit = "apple is red";

String color = fruit.substring(9);  // "red"

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String Methods

.substring(int beginIndex, int endIndex)

String fruit = "apple is red";

String noun = fruit.substring(0, 5); // "apple"
String verb = fruit.substring(6, 8); // "is"
String adjective = fruit.substring(9, fruit.length()); // "red"

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String Methods

.trim()

String words = "  apple is   ";
String trimmedWord = words.trim(); // "apple is"

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String Methods

.compareTo(String otherString)

"b".compareTo("a"); // 1
"b".compareTo("b"); // 0
"b".compareTo("c"); // -1

"10".compareTo("2"); // -1

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String concatenation

Combining strings

String name = "Moana";
String greeting = "Hello, " + name + "!"; // "Hello, Moana!"

String greeting2 = "Hello, ".concat(name).concat("!");

String greeting3 = String.join(" ","Hello,", name, "!");

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String concatenation

String and number/decimal

double pi = 3.14;
String message = "Pi is " + pi; // "Pi is 3.14"
String message2 = pi + " is pi"; // "3.14 is pi"

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Equality

String fruit1 = "apple";
String fruit2 = "apple";
String fruit3 = "Apple";

fruit1.equals(fruit2);

fruit1.equals(fruit3);
fruit1.equalsIgnoreCase(fruit3);

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Equality

Don’t use == to test for equality

String num = "3";
String num2 = Integer.toString(3);

num == num2;

num.equals(num2);

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Empty vs Null

String name = null;
System.out.println("My name is " + name); // "My name is null"
name.length(); // ERROR!!!!!


String name2 = "";
System.out.println("My name is " + name2); // "My name is "
name2.length(); // 0

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Checking if there is a value

public static boolean hasValue(String value) {
    if (value != null && value.trim().length() > 0) {
        return true;
    } else {
        return false;
    }
}

System.out.println(hasValue(null)); //false
System.out.println(hasValue("")); //false
System.out.println(hasValue("   ")); //false
System.out.println(hasValue("a")); //true

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Strings are immutable

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Concat + enation

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StringBuilder()

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Building Strings

Using the StringBuilder class allows you to build a string from many small pieces.

StringBuilder builder = new StringBuilder("ap");

builder.append('p'); // appends a single character
builder.append("le"); // appends a string

String completedString = builder.toString(); // "apple"

StringBuilder API

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Building Strings

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Strings from Objects

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toString method

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Overriding toString

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String operations

Read String API for more methods

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String Formatting

double total = 10.00 - 9.33;
System.out.println(total); //0.6699999999999999

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String Formatting

double total = 10.00 - 9.33;

String formattedTotal = String.format("Total is %,15.2f", total);
System.out.println(formattedTotal); //Total is            0.67

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String Formatting

"%[argument_index$][flags][min width][.precision]conversion"

The only field that is required is conversion

How to format String

String Formatting

"%[argument_index$][flags][min width][.precision]conversion"

| Specifier | Applies to | Output| | ——— | ——– | —– | | %b | Any type | true if non-null, false if null | | %c | character | character | | %s | any type | String value |

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String Formatting

"%[argument number] [flags][width].[precision][type]"

| Specifier | Applies to | Output| | ——— | ——– | —– | | %d | integer (incl. byte, short, int, long, bigint) | Decimal Integer | | %e | floating point | decimal number in scientific notation | | %f | floating point | decimal number |

String format = "Total is %,15.2f"

Pads with space, group with comma, with minimum with of 15 and precision of 2. Conversion type is float.

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Ways to format

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Useful Resources

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Codepoint

Once upon a time, there was ASCII. It assigns codes between 0 and 127 to all English letters, the decimal digits, and many symbols.

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Codepoint

But what about Russian, Japanese, and Chinese characters?

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Codepoint

Unicode to the rescue!

It assigns each character in all of the writing systems ever devised a unique 16-bit code between 0 and 65535.

When you see this it will usually be in hexidecimal from 0x0000 to 0xFFFF but Java supports encoding up to 0x10FFFF

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Codepoint

Unicode in Java

String symbol = "\ud835\udd46"; // 𝕆
symbol.length(); // 2
symbol.codePointCount(0, symbol.length()); // 1

List of Unicode character

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A peek at Regular Expressions

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Basic symbols

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Examples

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Regex sites

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