diff --git a/EscapeNestedLoops.java b/EscapeNestedLoops.java new file mode 100644 index 0000000..24546bd --- /dev/null +++ b/EscapeNestedLoops.java @@ -0,0 +1,26 @@ +// Java - How to Break out of Nested For Loops + +class EscapeNestedLoops { + public static void main(String[] args) { + + for(int x=0; x<8; x++) { + for(int y=1; y<4; y++) { + System.out.println(x + " " + y + " " + x*y); + if(x * y > 5) + break; + } + } + + System.out.println(" "); + + xLoop: + for(int x=0; x<8; x++) { + for(int y=1; y<4; y++) { + System.out.println(x + " " + y + " " + x*y); + if(x * y > 5) + break xLoop; + } + } + + } +} \ No newline at end of file diff --git a/ListToArray.java b/ListToArray.java new file mode 100644 index 0000000..f78124a --- /dev/null +++ b/ListToArray.java @@ -0,0 +1,45 @@ +// Java: convert ArrayList to String[] +import java.util.ArrayList; +import java.util.Arrays; +import java.util.List; +import java.util.stream.*; + +class ListToArray { + public static void main(String[] args) { + // create Array + String[] array = {"Bugatti", "Ferarri", "Lamborghini", "Rolls Royce"}; + + // 3 ways to print Array + System.out.println(Arrays.toString(array)); + + for(String s : array) { + System.out.print(s + ", "); + } + System.out.println(); + + Stream.of(array) + .forEach(System.out::println); + + // 2 ways to convert Array to ArrayList + List arrayList = new ArrayList<>(Arrays.asList(array)); + System.out.println("arrayList: " + arrayList); + + List arrayList2 = new ArrayList<>(List.of(array)); + System.out.println("arrayList2: " + arrayList2); + + // convert ArrayList to Array + String[] array2 = arrayList.toArray(new String[0]); + + // print Array + Stream.of(array2) + .forEach(System.out::println); + + } +} + + + + + + + diff --git a/MapFunctions.java b/MapFunctions.java new file mode 100644 index 0000000..0d17ff8 --- /dev/null +++ b/MapFunctions.java @@ -0,0 +1,71 @@ +// Java HashMap +// Joe James 2023 + +import java.util.Map; +import java.util.HashMap; +import java.util.Map.Entry; +import java.util.stream.*; + +class MapFunctions { + public static void main (String[] args) { + // 1. Create a HashMap, add kv pairs + Map ages = new HashMap(); + // OR, to initialize capaacity, + // Map ages = new HashMap(100); + ages.put("Avni",11); + ages.put("Bing", 12); + ages.put("Cassie", 13); + ages.put("Devarshi", 14); + System.out.println(ages); + + // 2. Get an item from the map + String person = "Cassie"; + System.out.println(person + " : " + ages.get(person)); + System.out.println("Frank" + " : " + ages.getOrDefault("Frank", 0)); + + // 3. Check for membership + System.out.println("Contains key Avni?: " + ages.containsKey("Avni")); + System.out.println("Contains value 23?: " + ages.containsValue(23)); + + // 4. Remove an item from the map + ages.remove("Bing"); + System.out.println(ages); + ages.remove("Devarshi", 41); + System.out.println(ages); + + // 5. Get count of items in map + System.out.println("Num Items = " + ages.size()); + + // 6. Remove all items from map + ages.clear(); + System.out.println("Empty map? " + ages.isEmpty()); + ages.put("Elena", 15); + ages.put("Frank", 16); + System.out.println(ages); + + // 7. Conditional add & replace + ages.putIfAbsent("George", 23); + ages.putIfAbsent("Elena", 5); + System.out.println(ages); + ages.replace("George", 23, 17); + ages.replace("George", 44, 55); + System.out.println(ages); + + // 8. Get collection of Values + System.out.println(ages.values()); + + // 9. Iterate keys using enhanced for loop + for (String key : ages.keySet()) { + System.out.println(key + " : " + ages.get(key)); + } + + // 10. Iterate KV pairs using enhanced for loop + for (Map.Entry pair : ages.entrySet()) { + System.out.println(pair.getKey() + " : " + pair.getValue()); + } + + // 11. Iterate KV pairs using Java 8 Stream API + ages.entrySet().stream().forEach(pair -> System.out.println(pair.getKey() + " : " + pair.getValue())); + + } +} \ No newline at end of file diff --git a/SplitString.java b/SplitString.java new file mode 100644 index 0000000..6f5a4fe --- /dev/null +++ b/SplitString.java @@ -0,0 +1,35 @@ +// Java: Split a String at char +import java.util.Arrays; + +class SplitString { + + public static void main(String[] args) { + String s = "My dog ate my homework; Can I turn it in tomorrow?"; + + String[] ss = s.split(" "); + System.out.println(Arrays.toString(ss)); + + ss = s.split(";"); + System.out.println(Arrays.toString(ss)); + + // you must escape special chars because the split parameter is a regex + // special chars include \ . + ^ $ | ? * ( ) [ { + String t = "54.25-128.17"; + String[] tt = t.split("\\."); + System.out.println(Arrays.toString(tt)); + + // include multiple split chars inside brackets + tt = t.split("[.-]"); + System.out.println(Arrays.toString(tt)); + + } +} + + + + + + + + + diff --git a/StringToInt.java b/StringToInt.java new file mode 100644 index 0000000..adbf9a9 --- /dev/null +++ b/StringToInt.java @@ -0,0 +1,26 @@ +// Java - Convert String to an Int + +class StringToInt { + public static void main(String[] args) { + String s = "222"; + int i; + Integer integer; + + // returns an int + i = Integer.parseInt(s); + System.out.println(i + 1); + + // returns an Integer + integer = Integer.valueOf(s); + System.out.println(integer + 2); + + // Best Practice: safely returns an Integer + try { + integer = Integer.valueOf(s); + } catch (NumberFormatException e) { + integer = 0; + } + System.out.println(integer + 3); + } + +} \ No newline at end of file