从对象数组列表中获取最大值？

Question

Is there an easy way to get the max value from one field of an object in an arraylist of objects? For example, out of the following object, I was hoping to get the highest value for the Value field.

Example arraylist I want to get the max value for ValuePairs.mValue from.

ArrayList<ValuePairs> ourValues = new ArrayList<>();
outValues.add(new ValuePairs("descr1", 20.00));
outValues.add(new ValuePairs("descr2", 40.00));
outValues.add(new ValuePairs("descr3", 50.00));

Class to create objects stored in arraylist:

public class ValuePairs {

    public String mDescr;
    public double mValue;

    public ValuePairs(String strDescr, double dValue) {
        this.mDescr = strDescr;
        this.mValue = dValue;
    }
}

I'm trying to get the max value for mValue by doing something like (which I know is incorrect):

double dMax = Collections.max(ourValues.dValue);

dMax should be 50.00.

Answer 1

Use a Comparator with Collections.max() to let it know which is greater in comparison.

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Also See

• How to use custom Comparator

Answer 2

使用 Java 8，您可以将stream()与它的预定义max()函数和Comparator.comparing()功能与 lambda 表达式一起使用：

ValuePairs maxValue = values.stream().max(Comparator.comparing(v -> v.getMValue())).get();

Answer 3

This has been answered multiple time already, but since it's the first result on google I will give a Java 8 answer with an example.

Take a look at the stream feature. Then you can get the max form an List of Objects like this:

List<ValuePairs> ourValues = new ArrayList<>();

ourValues.stream().max(comparing(ValuePairs::getMValue)).get()

By the way in your example, the attributes should be private. You can then access them with a getter.

Answer 4

You should iterate over the list comparing/finding the max value O(N) . If you need to do this often replace the list with a PriorityQueue O(1) to find the max.

Answer 5

Here fist and last is intervals between two indexes of arraylist you can also get for a complete list by removing them and i=0 upto size of float list.

// for min value

public String getMinValue(ArrayList list, int first, int last) {

        List<Float> floatList = new ArrayList<>();

        for (int i = 0; i < list.size(); i++) {
            Float prova2 = ((Double) list.get(i)).floatValue();
            floatList.add(prova2);
        }
        float min = Float.MAX_VALUE;
        String minValue = "";

        for (int i = first; i < last; i++) {


            if (floatList.get(i) < min) {
                min = floatList.get(i);
            }
        }
        minValue = String.format("%.1f", min);
        return minValue;
    }

// for max value

    public String getMaxValue(List<Object> list, int first, int last) {

        List<Float> floatList = new ArrayList<>();

        for (int i = 0; i < list.size(); i++) {
            Float prova2 = ((Double) list.get(i)).floatValue();
            floatList.add(prova2);
        }

        float max = Float.MIN_VALUE;
        String maxValue = "";

        for (int i = first; i < last; i++) {


            if (floatList.get(i) > max) {
                max = floatList.get(i);
            }
        }
        maxValue = String.format("%.1f", max);
        return maxValue;
    }