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Join lists")]),t._v(" "),a("p",[t._v("Following ways can be used for joining lists without modifying source list(s).")]),t._v(" "),a("p",[t._v("First approach. Has more lines but easy to understand")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("List")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v(" newList "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ArrayList")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nnewList"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("addAll")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("listOne"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nnewList"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("addAll")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("listTwo"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Second approach. Has one less line but less readable.")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("List")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v(" newList "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ArrayList")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("listOne"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nnewList"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("addAll")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("listTwo"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Third approach. Requires third party "),a("a",{attrs:{href:"https://commons.apache.org/proper/commons-collections/apidocs/org/apache/commons/collections4/ListUtils.html",target:"_blank",rel:"noopener noreferrer"}},[t._v("Apache commons-collections"),a("OutboundLink")],1),t._v(" library.")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ListUtils")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("union")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("listOne"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("listTwo"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Using Streams the same can be achieved by")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("List")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v(" newList "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Stream")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("concat")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("listOne"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("stream")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" listTwo"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("stream")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("collect")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Collectors")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("toList")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("References. "),a("a",{attrs:{href:"https://docs.oracle.com/javase/8/docs/api/java/util/List.html#addAll-java.util.Collection-",target:"_blank",rel:"noopener noreferrer"}},[t._v("Interface List"),a("OutboundLink")],1)]),t._v(" "),a("h2",{attrs:{id:"removing-matching-items-from-lists-using-iterator"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#removing-matching-items-from-lists-using-iterator"}},[t._v("#")]),t._v(" Removing matching items from Lists using Iterator.")]),t._v(" "),a("p",[t._v("Above I noticed an example to remove items from a List within a Loop and I thought of another example that may come in handy this time using the "),a("code",[t._v("Iterator")]),t._v(" interface."),a("br"),t._v("\nThis is a demonstration of a trick that might come in handy when dealing with duplicate items in lists that you want to get rid of.")]),t._v(" "),a("p",[t._v("Note: This is only adding on to the "),a("strong",[t._v("Removing items from a List within a loop")]),t._v(" example:")]),t._v(" "),a("p",[t._v("So let's define our lists as usual")]),t._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[t._v('\n   String[] names = {"James","Smith","Sonny","Huckle","Berry","Finn","Allan"};\n    List<String> nameList = new ArrayList<>();\n\n    //Create a List from an Array\n    nameList.addAll(Arrays.asList(names));\n    \n    String[] removeNames = {"Sonny","Huckle","Berry"};\n    List<String> removeNameList = new ArrayList<>();\n\n    //Create a List from an Array\n    removeNameList.addAll(Arrays.asList(removeNames));\n\n')])])]),a("p",[t._v("The following method takes in two Collection objects and performs the magic of removing the elements in our "),a("code",[t._v("removeNameList")]),t._v(" that match with elements in "),a("code",[t._v("nameList")]),t._v(".")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token 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punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//remove the current Name or Item")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("Calling the method and passing in the "),a("code",[t._v("nameList")]),t._v(" and the "),a("code",[t._v("removeNameList")]),t._v("as follows "),a("code",[t._v("removeNames(nameList,removeNameList);")]),a("br"),t._v("\nWill produce the following output:")]),t._v(" "),a("blockquote"),t._v(" "),a("p",[t._v("Array List before removing names:\n**James Smith Sonny Huckle Berry Finn Allan**"),a("br"),t._v("\nArray List after removing names:\n**James Smith Finn Allan**")]),t._v(" "),a("p",[t._v("A simple neat use for Collections that may come in handy to remove repeating elements within lists.")]),t._v(" "),a("h2",{attrs:{id:"collections-and-primitive-values"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#collections-and-primitive-values"}},[t._v("#")]),t._v(" Collections and Primitive Values")]),t._v(" "),a("p",[t._v("Collections in Java only work for objects. I.e. there is no "),a("code",[t._v("Map<int, int>")]),t._v(" in Java. Instead, primitive values need to be "),a("strong",[t._v("boxed")]),t._v(" into objects, as in "),a("code",[t._v("Map<Integer, Integer>")]),t._v(". Java auto-boxing will enable transparent use of these collections:")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Map")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Integer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),t._v(" map "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("HashMap")]),a("span",{pre:!0,attrs:{class:"token generics"}},[a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(">")])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nmap"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("put")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("17")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Automatic boxing of int to Integer objects")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" map"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Automatic unboxing.")]),t._v("\n\n")])])]),a("p",[t._v("Unfortunately, the overhead of this is "),a("strong",[t._v("substantial")]),t._v(". A "),a("code",[t._v("HashMap<Integer, Integer>")]),t._v(" will require about 72 bytes per entry (e.g. on 64-bit JVM with compressed pointers, and assuming integers larger than 256, and assuming 50% load of the map). Because the actual data is only 8 bytes, this yields a massive overhead. Furthermore, it requires two level of indirection (Map -> Entry -> Value) it is unnecessarily slow.")]),t._v(" "),a("p",[t._v("There exist several libraries with optimized collections for primitive data types (that require only ~16 bytes per entry at 50% load, i.e. 4x less memory, and one level of indirection less), that can yield substantial performance benefits when using large collections of primitive values in Java.")]),t._v(" "),a("h2",{attrs:{id:"creating-your-own-iterable-structure-for-use-with-iterator-or-for-each-loop"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#creating-your-own-iterable-structure-for-use-with-iterator-or-for-each-loop"}},[t._v("#")]),t._v(" Creating your own Iterable structure for use with Iterator or for-each loop.")]),t._v(" "),a("p",[t._v("To ensure that our collection can be iterated using iterator or for-each loop, we have to take care of following steps:")]),t._v(" "),a("li",[t._v("The stuff we want to iterate upon has to be `Iterable` and expose\n`iterator()`.")]),t._v("\n1. 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