{"id":7621,"date":"2012-09-17T20:29:13","date_gmt":"2012-09-17T14:59:13","guid":{"rendered":"http:\/\/www.tothenew.com\/blog\/?p=7621"},"modified":"2014-12-17T09:24:04","modified_gmt":"2014-12-17T03:54:04","slug":"understanding-groovy-withlazydefault-and-witheagerdefault-methods","status":"publish","type":"post","link":"https:\/\/www.tothenew.com\/blog\/understanding-groovy-withlazydefault-and-witheagerdefault-methods\/","title":{"rendered":"Understanding Groovy 2.0 withLazyDefault and withEagerDefault methods"},"content":{"rendered":"

Sometimes there is need to get some default value in place of null values from a list, that was the reason I came across: withLazyDefault<\/strong> and withEagerDefault<\/strong> methods.
\n
\nMy use case consisted of a list of user names with possibility of null elements, hence wherever the element was null, I wanted to return \u201cunknown\u201d. Although there was other ways of doing the same, but most cleaner way was using withLazyDefault<\/strong>.
\n
\nThese methods are also useful when a list is accessed for a index which doesnot exist i.e. avoiding index out of bound exception. And for map, these methods are useful when map is accessed for a key, whose entry(key-value pair) does not exist.
\n
\nLets start with withLazyDefault<\/strong> method. We can also use withDefault<\/strong> instead of withLazyDefault<\/strong> because withDefault<\/strong> method calls withLazyDefault<\/strong> internally.<\/p>\n

[java]
\nList<String> languages = ["C","C++",null, "Flex","VB","Java"].withDefault{"Groovy"}<\/p>\n

println languages.get(2)<\/p>\n

\/\/Output : Groovy, (even though at index 2, value is null)
\n[\/java]<\/p>\n

As the value at index 2 was null, but because of default value set at initialization time, langauges.get(2) returned “Groovy” as value.<\/p>\n

Now, If a list is accessed for a index (lets say mth<\/sup> index) greater than languages.size()-1 (lets say nth<\/sup> index, list’s actual size), and if default value is set using withDefault<\/strong>(withLazyDefault), then list grows to the size (m+1). The gap in between is filled with null values, although access to list using any index in gap will return default value.<\/p>\n

e.g.<\/p>\n

[java]
\n List<String> languages = ["C","C++",null, "Flex","VB","Java"].withDefault{"Groovy"}<\/p>\n

println languages.size()
\n\/\/Output : 6<\/p>\n

println languages.get(10)
\n\/\/Output : Groovy<\/p>\n

println languages.size()
\n\/\/Output : 11<\/p>\n

println languages
\n\/\/ [C, C++, null, Flex, VB, Java, null, null, null, null, Groovy]<\/p>\n

println languages.get(8)
\n\/\/ Output : Groovy<\/p>\n

[\/java]<\/p>\n

As you will see, no indexOutOfBoundException will occur and size will grow to the specified index.<\/p>\n

Usage with Map:<\/p>\n

[java]
\nMap<String,Integer> languages = ["C":1,"C++":3, "Flex":5,"VB":4,"Java":5].withDefault{10}<\/p>\n

println languages.size()
\n\/\/Output : 5<\/p>\n

println languages.get("Groovy")
\n\/\/Output : 10<\/p>\n

println languages.get("COBOL")
\n\/\/Output : 10<\/p>\n

println languages.size()
\n\/\/Output : 7<\/p>\n

println languages
\n\/\/Output : [C:1, C++:3, Flex:5, VB:4, Java:5, Groovy:10, COBOL:10]<\/p>\n

[\/java]<\/p>\n

A new entry gets added in the map for the key whose entry (key-value pair) does not exist in Map with default value.<\/p>\n

The only difference between withLazyDefault<\/strong> and withEagerDefault<\/strong> is that the gap between actual list and new list will be populated with default value in case of withEagerDefault instead of null values as in case of withLazyDefault method.<\/p>\n

In case of withLazyDefault<\/strong>:<\/p>\n

[java]
\nList<String> languages = ["C","C++",null, "Flex","VB","Java"].withLazyDefault{"Groovy"}<\/p>\n

println languages.get(10)
\n\/\/ Output : Groovy<\/p>\n

println languages
\n\/\/Output: [C, C++, null, Flex, VB, Java, null, null, null, null, Groovy]
\n[\/java]<\/p>\n

In case of withEagerDefault<\/strong>:<\/p>\n

[java]
\nList<String> languageList = ["C","C++",null, "Flex","VB","Java"].withEagerDefault{"Groovy"}<\/p>\n

println languageList.get(10)
\n\/\/Output : Groovy<\/p>\n

println languageList \/\/ Output: [C, C++, null, Flex, VB, Java, Groovy, Groovy, Groovy, Groovy, Groovy]
\n[\/java]<\/p>\n

Hope it would help!!!<\/p>\n

Divya Setia<\/a>
\ndivya@intelligrape.com<\/a>
\nhttps:\/\/twitter.com\/divs157<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Sometimes there is need to get some default value in place of null values from a list, that was the reason I came across: withLazyDefault and withEagerDefault methods. My use case consisted of a list of user names with possibility of null elements, hence wherever the element was null, I wanted to return \u201cunknown\u201d. Although […]<\/p>\n","protected":false},"author":29,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"iawp_total_views":7},"categories":[7],"tags":[9,977,979,978],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.tothenew.com\/blog\/wp-json\/wp\/v2\/posts\/7621"}],"collection":[{"href":"https:\/\/www.tothenew.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.tothenew.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.tothenew.com\/blog\/wp-json\/wp\/v2\/users\/29"}],"replies":[{"embeddable":true,"href":"https:\/\/www.tothenew.com\/blog\/wp-json\/wp\/v2\/comments?post=7621"}],"version-history":[{"count":0,"href":"https:\/\/www.tothenew.com\/blog\/wp-json\/wp\/v2\/posts\/7621\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.tothenew.com\/blog\/wp-json\/wp\/v2\/media?parent=7621"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.tothenew.com\/blog\/wp-json\/wp\/v2\/categories?post=7621"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.tothenew.com\/blog\/wp-json\/wp\/v2\/tags?post=7621"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}