Queries using Java API

hello,i tried adding to my code an ES query using Java API but i failed because of the lack of documentation and i would use some help. Here's the query i need to transform using Java API :
"{
"query":{
"has_child": {
"type": "data",
"score_type" : "avg",
"query" : {
"query_string": {
"query": " abcdef" } } } }}"