Java 对HashMap<String,Double>排序

比较类写法

package org.test;

import java.util.Comparator;
import java.util.Map;

public class ByValueComparator implements Comparator<String> {
Map<String, Double> base_map;

public ByValueComparator(Map<String, Double> base_map) {
this.base_map = base_map;
}

public int compare(String arg0, String arg1) {
if (!base_map.containsKey(arg0) || !base_map.containsKey(arg1)) {
return 0;
}

if (base_map.get(arg0) < base_map.get(arg1)) {
return 1;
} else if (base_map.get(arg0) > base_map.get(arg1)) {
return -1;
} else {
return 0;
}
}
}

使用方法

maps.put("a", new Double(1));
//maps.put("b", new Double(2));
ByValueComparator bvc = new ByValueComparator(maps);
ArrayList<String> keys = new ArrayList<String>(maps.keySet());
Collections.sort(keys, bvc);

如果不按照ByValueComparator写法，则会报错：Comparison method violates its general contract。

详细的算法分析见图解JDK7的Comparison method violates its general contract异常