Java 8 使用Java8从映射到列表收集数据
请帮助我使用Java8Map-filter-sort-collect代码 Info.javaJava 8 使用Java8从映射到列表收集数据,java-8,Java 8,请帮助我使用Java8Map-filter-sort-collect代码 Info.java public class Info { private final String name; private final String desc; private String version = null; @Override public boolean equals(Object that) { if (that == null) { return false;
public class Info {
private final String name;
private final String desc;
private String version = null;
@Override
public boolean equals(Object that) {
if (that == null) {
return false;
}
if (that instanceof Info) {
Info other = (Info) that;
return Objects.equals(this.name, other.name) &&
Objects.equals(this.desc, other.desc) &&
Objects.equals(this.version, other.version);
} else {
return false;
}
}
public boolean equalsWithoutVersion(Object that) {
if (that == null) {
return false;
}
if (that instanceof Info) {
Info other = (Info) that;
return Objects.equals(this.name, other.name) &&
Objects.equals(this.desc, other.desc);
} else {
return false;
}
}
@Override
public int hashCode() {
int hash = 13;
hash = (hash * 7) + name.hashCode();
hash = (hash * 7) + desc.hashCode();
if (version != null)
hash = (hash * 7) + version.hashCode();
return hash;
}
@Override
public String toString() {
String versionString = version == null ? "latest" : version;
return String.format("Name: %s Desc: %s Key Type: %s Version: %s", this.name, this.desc, this.keyType.name(), versionString);
}
}
public class Value implements Comparable<Value> {
private String data;
private String version;
public Value(String version, String data) {
this.version = version;
this.data = data;
}
@Override
public int compareTo(Value o) {
return (Integer.parseInt(this.version) > Integer.parseInt(o.version)) ? -1
: (Integer.parseInt(this.version) < Integer.parseInt(o.version)) ? 1
: 0;
}
}
public class Cache {
private final Map<Info, Value> dataMap = new HashMap<>();
...
private Value getlatestVersionFromCache(Info info) {
List<Value> values = dataMap.entrySet().stream()
.filter(p -> p.getKey().equalsWithoutVersion(info))
.sorted(Map.Entry.comparingByValue())
.map(x::getValue))
.collect(Collectors.toList());
return values.isEmpty() ? null : values.get(0);
}
}
Value.java
public class Info {
private final String name;
private final String desc;
private String version = null;
@Override
public boolean equals(Object that) {
if (that == null) {
return false;
}
if (that instanceof Info) {
Info other = (Info) that;
return Objects.equals(this.name, other.name) &&
Objects.equals(this.desc, other.desc) &&
Objects.equals(this.version, other.version);
} else {
return false;
}
}
public boolean equalsWithoutVersion(Object that) {
if (that == null) {
return false;
}
if (that instanceof Info) {
Info other = (Info) that;
return Objects.equals(this.name, other.name) &&
Objects.equals(this.desc, other.desc);
} else {
return false;
}
}
@Override
public int hashCode() {
int hash = 13;
hash = (hash * 7) + name.hashCode();
hash = (hash * 7) + desc.hashCode();
if (version != null)
hash = (hash * 7) + version.hashCode();
return hash;
}
@Override
public String toString() {
String versionString = version == null ? "latest" : version;
return String.format("Name: %s Desc: %s Key Type: %s Version: %s", this.name, this.desc, this.keyType.name(), versionString);
}
}
public class Value implements Comparable<Value> {
private String data;
private String version;
public Value(String version, String data) {
this.version = version;
this.data = data;
}
@Override
public int compareTo(Value o) {
return (Integer.parseInt(this.version) > Integer.parseInt(o.version)) ? -1
: (Integer.parseInt(this.version) < Integer.parseInt(o.version)) ? 1
: 0;
}
}
public class Cache {
private final Map<Info, Value> dataMap = new HashMap<>();
...
private Value getlatestVersionFromCache(Info info) {
List<Value> values = dataMap.entrySet().stream()
.filter(p -> p.getKey().equalsWithoutVersion(info))
.sorted(Map.Entry.comparingByValue())
.map(x::getValue))
.collect(Collectors.toList());
return values.isEmpty() ? null : values.get(0);
}
}
您发布的代码中有几处遗漏和错误,但
filter
语句实际上没有问题
以下内容通过了编译:
List<Value> values = dataMap.entrySet()
.stream()
.filter(p -> p.getKey().equalsWithoutVersion(info))
.sorted(Map.Entry.comparingByValue())
.map(Map.Entry::getValue) // was .map(x::getValue)) - x is not defined anywhere, so
// I assumed you meant Map.Entry::getValue
.collect(Collectors.toList());
List values=dataMap.entrySet()
.stream()
.filter(p->p.getKey().equalsWithoutVersion(信息))
.sorted(Map.Entry.comparingByValue())
.map(map.Entry::getValue)//was.map(x::getValue))-x未在任何地方定义,因此
//我以为你指的是Map.Entry::getValue
.collect(Collectors.toList());
课程信息{
公共静态最终双预测等于忽略版本=
(一,二)->one.getName().equals(二.getName())&&one.getDesc().equals(二.getDesc());
私有最终字符串名;
私有最终字符串描述;
私有字符串版本;
}
private final Map dataMap=new HashMap();
公共值getlatestVersionFromCache(信息){
Value=null;
对于(Map.Entry:dataMap.entrySet())
if(Info.IS_EQUAL_IGNORE_VERSION.test(entry.getKey(),Info))
if(value==null | | Integer.parseInt(entry.getValue().getVersion())>Integer.parseInt(value.getVersion())
value=entry.getValue();
返回值;
}
注:
谓词
。并将其定义为目标类中的静态方法版本
。似乎它应该是一个整数而不是字符串equals
方法Java8
流是不正确的我怀疑你的解决方案。我想你可以用简单的方法来做。因此,首先在
Value
类中将version
类型更改为Integer
(在compareTo()方法中将其转换为Integer)。还可以在getlatestVersionFromCache()
方法中将方法签名更改为可选的
另外,我认为您不需要排序dataMap
private Optional<Value> getlatestVersionFromCache(Info info) {
Map<Value,Integer> result = dataMap.entrySet()
.stream()
.filter(p -> p.getKey().equalsWithoutVersion(info))
.collect(Collectors.toMap(Map.Entry::getValue, entry -> entry.getValue().getVersion(), Integer::min));
Optional<Value> latestValue = result.keySet()
.stream()
.min(Comparator.comparingInt(key -> key.getVersion()));
return latestValue;
}
问题是这里额外的偏执:.map(x::getValue))
stream()
出现在我的代码中,尽管我没有在一开始就提出这个问题。无论如何,感谢私钥getlatestVersionFromCache(){…}
中的键
结构是什么?为什么将版本
作为字符串获取?此行的作用是什么.collect(Collectors.toMap(Map.Entry::getValue,Entry->Entry.getValue().getVersion(),Integer::min))
@cppcoder它根据version属性计算最小值对象。但我认为这更有效Optional latestValue=dataMap.entrySet().stream().filter(p->p.getKey().equalsWithoutVersion(info)).min(Comparator.comparingit(entry->entry.getValue().getVersion())代码>和latestValue.get().getValue()代码>