简单地用循环就可以啊
String[] days={"周六","周日","周一"};
String[] place={"森林公园","新华书店"};
String[] thing={"钓鱼","看书"};
for(int i=0;i<days.length;i++){
     for(int j=0;j<place.length;j++){
         for(int k=0;k<thing.length;k++){
             String result=days[i]+"一起去"+place[j]+thing[k];
             System.out.println(result);
         }
     }
}