在Java 8中,如何转换Map< K,V>到另一个地图< K,V>使用lambda? [英] In Java 8 how do I transform a Map<K,V> to another Map<K,V> using a lambda?
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问题描述
Map< String,Column> newColumnMap = new HashMap<>();
originalColumnMap.entrySet()。stream()。forEach(x - > newColumnMap.put(x.getKey(),new Column(x.getValue())))
但我确信必须有一个更好的方式来做,我会感激一些建议。
解决方案
您可以使用收藏者:
import java.util。*;
import java.util.stream.Collectors;
public class Defensive {
public static void main(String [] args){
Map< String,Column> original = new HashMap<>();
original.put(foo,new Column());
original.put(bar,new Column());
映射< String,Column> copy = original.entrySet()
.stream()
.collect(Collectors.toMap(Map.Entry :: getKey,
e - > new Column(e.getValue())) );
System.out.println(original);
System.out.println(copy);
}
static class Column {
public Column(){}
public Column(column c){}
}
}
I've just started looking at Java 8 and to try out lambdas I thought I'd try to rewrite a very simple thing I wrote recently. I need to turn a Map of String to Column into another Map of String to Column where the Column in the new Map is a defensive copy of the Column in the first Map. Column has a copy constructor. The closest I've got so far is:
Map<String, Column> newColumnMap= new HashMap<>();
originalColumnMap.entrySet().stream().forEach(x -> newColumnMap.put(x.getKey(), new Column(x.getValue())));
but I'm sure there must be a nicer way to do it and I'd be grateful for some advice.
解决方案
You could use a Collector:
import java.util.*;
import java.util.stream.Collectors;
public class Defensive {
public static void main(String[] args) {
Map<String, Column> original = new HashMap<>();
original.put("foo", new Column());
original.put("bar", new Column());
Map<String, Column> copy = original.entrySet()
.stream()
.collect(Collectors.toMap(Map.Entry::getKey,
e -> new Column(e.getValue())));
System.out.println(original);
System.out.println(copy);
}
static class Column {
public Column() {}
public Column(Column c) {}
}
}
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