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"),a("p",[t._v("The "),a("code",[t._v("Collections")]),t._v(" class provides two useful methods for creating Lists without a "),a("code",[t._v("List")]),t._v(" variable:")]),t._v(" "),a("ul",[a("li",[a("code",[t._v("emptyList()")]),t._v(": returns an empty list.")]),t._v(" "),a("li",[a("code",[t._v("singletonList(T)")]),t._v(": creates a list of type T and adds the element specified.")])]),t._v(" "),a("p",[t._v("And a method which uses an existing "),a("code",[t._v("List")]),t._v(" to fill data in:")]),t._v(" "),a("ul",[a("li",[a("code",[t._v("addAll(L, T...)")]),t._v(": adds all the specified elements to the list passed as the first parameter.")])]),t._v(" "),a("p",[a("strong",[a("strong",[t._v("Examples:")])])]),t._v(" "),a("h2",{attrs:{id:"positional-access-operations"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#positional-access-operations"}},[t._v("#")]),t._v(" Positional Access Operations")]),t._v(" "),a("p",[t._v("The List API has eight methods for positional access operations:")]),t._v(" "),a("ul",[a("li",[a("code",[t._v("add(T type)")])]),t._v(" "),a("li",[a("code",[t._v("add(int index, T type)")])]),t._v(" "),a("li",[a("code",[t._v("remove(Object o)")])]),t._v(" "),a("li",[a("code",[t._v("remove(int index)")])]),t._v(" "),a("li",[a("code",[t._v("get(int index)")])]),t._v(" "),a("li",[a("code",[t._v("set(int index, E element)")])]),t._v(" "),a("li",[a("code",[t._v("int indexOf(Object o)")])]),t._v(" "),a("li",[a("code",[t._v("int lastIndexOf(Object o)")])])]),t._v(" "),a("p",[t._v("So, if we have a List:")]),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(" strings "),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("\n\n")])])]),a("p",[t._v('And we wanted to add the strings "Hello world!" and "Goodbye world!" to it, we would do it as such:')]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[t._v("strings"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("add")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Hello world!"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nstrings"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("add")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Goodbye world!"')]),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('And our list would contain the two elements.\nNow lets say we wanted to add "Program starting!" at the '),a("strong",[t._v("front")]),t._v(" of the list. We would do this like this:")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[t._v("strings"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("add")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Program starting!"')]),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",[a("strong",[t._v("NOTE: The first element is 0.")])]),t._v(" "),a("p",[t._v('Now, if we wanted to remove the "Goodbye world!" line, we could do it like this:')]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[t._v("strings"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("remove")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Goodbye world!"')]),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('And if we wanted to remove the first line (which in this case would be "Program starting!", we could do it like this:')]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[t._v("strings"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("remove")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),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("Note:")]),t._v(" "),a("li",[t._v("\nAdding and removing list elements modify the list, and this can lead to a `ConcurrentModificationException` if the list is being iterated concurrently.\n")]),t._v(" "),a("li",[t._v("\nAdding and removing elements can be `O(1)` or `O(N)` depending on the list class, the method used, and whether you are adding / removing an element at the start, the end, or in the middle of the list.\n")]),t._v(" "),a("p",[t._v("In order to retrieve an element of the list at a specified position you can use the "),a("code",[t._v("E get(int index);")]),t._v(" method of the List API. For example:")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[t._v("strings"),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("0")]),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("will return the first element of the list.")]),t._v(" "),a("p",[t._v("You can replace any element at a specified position by using the "),a("code",[t._v("set(int index, E element);")]),t._v(". For example:")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[t._v("strings"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("set")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"This is a replacement"')]),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('This will set the String "This is a replacement" as the first element of the list.')]),t._v(" "),a("p",[t._v("Note:\nThe set method will overwrite the element at the position 0. It will not add the new String at the position 0 and push the old one to the position 1.")]),t._v(" "),a("p",[t._v("The "),a("code",[t._v("int indexOf(Object o);")]),t._v(" returns the position of the first occurrence of the object passed as argument. If there are no occurrences of the object in the list then the -1 value is returned. In continuation of the previous example if you call:")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[t._v("strings"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("indexOf")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"This is a replacement"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[t._v('the 0 is expected to be returned as we set the String "This is a replacement" in the position 0 of our list.\nIn case where there are more than one occurrence in the list when '),a("code",[t._v("int indexOf(Object o);")]),t._v(" is called then as mentioned the index of the first occurrence will be returned. By calling the "),a("code",[t._v("int lastIndexOf(Object o)")]),t._v(' you can retrieve the index of the last occurrence in the list. So if we add another "This is a replacement":')]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[t._v("strings"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("add")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"This is a replacement"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nstrings"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("lastIndexOf")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"This is a replacement"')]),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("This time the 1 will be returned and not the 0;")]),t._v(" "),a("h2",{attrs:{id:"iterating-over-elements-in-a-list"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#iterating-over-elements-in-a-list"}},[t._v("#")]),t._v(" Iterating over elements in a list")]),t._v(" "),a("p",[t._v('For the example, lets say that we have a List of type String that contains four elements: "hello, ", "how ", "are ", "you?"')]),t._v(" "),a("p",[t._v("The best way to iterate over each element is by using a for-each loop:")]),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 keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("printEachElement")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),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(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("for")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),t._v(" s "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("s"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),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"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("Which would print:")]),t._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[t._v("hello"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v("\nhow\nare\nyou"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("?")]),t._v("\n\n")])])]),a("p",[t._v("To print them all in the same line, you can use a StringBuilder:")]),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 keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("printAsLine")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),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(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("StringBuilder")]),t._v(" builder "),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("StringBuilder")]),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    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("for")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("String")]),t._v(" s "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" list"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        builder"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("append")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("s"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),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    "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("System")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("println")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("builder"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("toString")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token 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Warning: this approach is inefficient for linked lists.")]),t._v(" "),a("h2",{attrs:{id:"removing-elements-from-list-b-that-are-present-in-the-list-a"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#removing-elements-from-list-b-that-are-present-in-the-list-a"}},[t._v("#")]),t._v(" Removing elements from list B that are present in the list A")]),t._v(" "),a("p",[t._v("Lets suppose you have 2 Lists A and B, and you want to remove from "),a("strong",[t._v("B")]),t._v(" all the elements that you have in "),a("strong",[t._v("A")]),t._v("  the method in this case is")]),t._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[t._v("\nList.removeAll(Collection c);\n\n")])])]),a("p",[a("strong",[t._v("#Example:")])]),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 keyword"}},[t._v("public")]),t._v(" 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