2024-08-07

One-liner

"Love is actually simple; the hard part is accepting it." — "Shaman King" · hitokoto

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Java Map.getOrDefault

You can achieve this by performing a null check directly in the vo.setA() method. Here's an example demonstrating how to check if map.get("A") is null, set it to 0 if it is, or set it to the value of map.get("A") otherwise.

Assuming your VO class is named MyVO and its a property has a setA method, here’s the code:

import java.util.Map;

public class Main {
    public static void main(String[] args) {
        // Create a sample VO object
        MyVO vo = new MyVO();

        // Create a sample Map
        Map<String, Integer> map = Map.of("A", 10, "B", 20);

        // Use map.getOrDefault to set the value of 'a'
        vo.setA(map.getOrDefault("A", 0));

        // Print the value of 'a' in VO
        System.out.println("Value of 'a' in VO: " + vo.getA());
    }
}

class MyVO {
    private int a;

    public int getA() {
        return a;
    }

    public void setA(int a) {
        this.a = a;
    }
}

In this example:

1. map.getOrDefault("A", 0) returns the value associated with key "A" if it exists, or 0 if it doesn’t.
2. vo.setA(map.getOrDefault("A", 0)) directly sets the a property.

Java list to map

To place count and exp into another class Fin, and add a List<Fin> field to MyVO class, and then calculate the total sum of count and exp for each status, you can do it as follows:

Define Fin class and the modified MyVO class:

import java.math.BigDecimal;
import java.util.List;

class Fin {
    private BigDecimal count;
    private BigDecimal exp;

    // Constructors, getters, and setters
    public Fin(BigDecimal count, BigDecimal exp) {
        this.count = count;
        this.exp = exp;
    }

    public BigDecimal getCount() {
        return count;
    }

    public void setCount(BigDecimal count) {
        this.count = count;
    }

    public BigDecimal getExp() {
        return exp;
    }

    public void setExp(BigDecimal exp) {
        this.exp = exp;
    }
}

enum Status {
    PLAN,
    IN,
    COM
}

class MyVO {
    private String name;
    private Status status;
    private List<Fin> fins;

    // Constructors, getters, and setters
    public MyVO(String name, Status status, List<Fin> fins) {
        this.name = name;
        this.status = status;
        this.fins = fins;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Status getStatus() {
        return status;
    }

    public void setStatus(Status status) {
        this.status = status;
    }

    public List<Fin> getFins() {
        return fins;
    }

    public void setFins(List<Fin> fins) {
        this.fins = fins;
    }
}

Convert List<MyVO> to Map<Status, BigDecimal> and calculate the total sum of count and exp for all Fin objects:

import java.math.BigDecimal;
import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        // Create sample Fin objects
        List<Fin> fins1 = Arrays.asList(
            new Fin(new BigDecimal("10"), new BigDecimal("5")),
            new Fin(new BigDecimal("20"), new BigDecimal("10"))
        );

        List<Fin> fins2 = Arrays.asList(
            new Fin(new BigDecimal("15"), new BigDecimal("7")),
            new Fin(new BigDecimal("25"), new BigDecimal("12"))
        );

        List<Fin> fins3 = Arrays.asList(
            new Fin(new BigDecimal("30"), new BigDecimal("15"))
        );

        // Create sample VO objects
        List<MyVO> list = Arrays.asList(
            new MyVO("A", Status.PLAN, fins1),
            new MyVO("B", Status.IN, fins2),
            new MyVO("C", Status.PLAN, fins3)
        );

        // Convert List<MyVO> to Map<Status, BigDecimal>, summing count and exp for all Fin objects
        Map<Status, BigDecimal> statusSumMap = list.stream()
                                                   .collect(Collectors.groupingBy(
                                                       MyVO::getStatus, // Group by status
                                                       Collectors.reducing(
                                                           BigDecimal.ZERO,
                                                           vo -> vo.getFins().stream()
                                                                   .map(fin -> fin.getCount().add(fin.getExp()))
                                                                   .reduce(BigDecimal.ZERO, BigDecimal::add), // Sum count and exp
                                                           BigDecimal::add // Combine results for the same status
                                                       )
                                                   ));

        // Print the results
        statusSumMap.forEach((status, totalSum) -> System.out.println("Status: " + status + ", Total Sum: " + totalSum));
    }
}

In this example:

1. list.stream() converts the list to a stream.
2. collect(Collectors.groupingBy(...)) collects the stream into a Map:
   • MyVO::getStatus groups by status.
   • Collectors.reducing(...) sums count and exp for each MyVO object’s fins list and combines results for the same status.

Complete Example Code:

import java.math.BigDecimal;
import java.util.*;
import java.util.stream.Collectors;

class Fin {
    private BigDecimal count;
    private BigDecimal exp;

    // Constructors, getters, and setters
    public Fin(BigDecimal count, BigDecimal exp) {
        this.count = count;
        this.exp = exp;
    }

    public BigDecimal getCount() {
        return count;
    }

    public void setCount(BigDecimal count) {
        this.count = count;
    }

    public BigDecimal getExp() {
        return exp;
    }

    public void setExp(BigDecimal exp) {
        this.exp = exp;
    }
}

enum Status {
    PLAN,
    IN,
    COM
}

class MyVO {
    private String name;
    private Status status;
    private List<Fin> fins;

    // Constructors, getters, and setters
    public MyVO(String name, Status status, List<Fin> fins) {
        this.name = name;
        this.status = status;
        this.fins = fins;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Status getStatus() {
        return status;
    }

    public void setStatus(Status status) {
        this.status = status;
    }

    public List<Fin> getFins() {
        return fins;
    }

    public void setFins(List<Fin> fins) {
        this.fins = fins;
    }
}

public class Main {
    public static void main(String[] args) {
        // Create sample Fin objects
        List<Fin> fins1 = Arrays.asList(
            new Fin(new BigDecimal("10"), new BigDecimal("5")),
            new Fin(new BigDecimal("20"), new BigDecimal("10"))
        );

        List<Fin> fins2 = Arrays.asList(
            new Fin(new BigDecimal("15"), new BigDecimal("7")),
            new Fin(new BigDecimal("25"), new BigDecimal("12"))
        );

        List<Fin> fins3 = Arrays.asList(
            new Fin(new BigDecimal("30"), new BigDecimal("15"))
        );

        // Create sample VO objects
        List<MyVO> list = Arrays.asList(
            new MyVO("A", Status.PLAN, fins1),
            new MyVO("B", Status.IN, fins2),
            new MyVO("C", Status.PLAN, fins3)
        );

        // Convert List<MyVO> to Map<Status, BigDecimal>, summing count and exp for all Fin objects
        Map<Status, BigDecimal> statusSumMap = list.stream()
                                                   .collect(Collectors.groupingBy(
                                                       MyVO::getStatus, // Group by status
                                                       Collectors.reducing(
                                                           BigDecimal.ZERO,
                                                           vo -> vo.getFins().stream()
                                                                   .map(fin -> fin.getCount().add(fin.getExp()))
                                                                   .reduce(BigDecimal.ZERO, BigDecimal::add), // Sum count and exp
                                                           BigDecimal::add // Combine results for the same status
                                                       )
                                                   ));

        // Print the results
        statusSumMap.forEach((status, totalSum) -> System.out.println("Status: " + status + ", Total Sum: " + totalSum));
    }
}

This code shows how to convert a List<MyVO> to a Map<Status, BigDecimal> and calculate the total sum of count and exp for each status.