仅获取与条件匹配的ArrayList的第一个元素

Question

我一直试图找到可能的答案,但没有发现.

我有ArrayList一整套自定义对象.他们的一个领域是boolean.

我想把这个对象放在第一位,保留其余的元素

例如,如果我有这个列表并且obj5是将此布尔值设置为true的那个:

obj3, obj2, obj5, obj7, obj9

我想得到这个:

obj5, obj3, obj2, obj7, obj9

编辑:不能使用LAMBDAS,JAVA 6

编辑2:请注意,列表的其余部分必须遵守旧订单

编辑3:简而言之,我需要这个程序输出[B,A,C,D,E]:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Trip {

@Override
public String toString() {
    return name;
}

private String name;
private boolean freeCancellation;


public Trip(String name, boolean freeCancellation) {
    this.name = name;
    this.freeCancellation = freeCancellation;
}

static Comparator<Trip> myOrder = new Comparator<Trip>() {
    public int compare(Trip a, Trip b) {
        if (a.freeCancellation == b.freeCancellation) return 0;
        return a.freeCancellation ? -1 : 1;
    }
};

public static void main(String [] args){
    Trip t1 = new Trip("A", false);
    Trip t2 = new Trip("B", true);
    Trip t3 = new Trip("C", false);
    Trip t4 = new Trip("D", true);
    Trip t5 = new Trip("E", false);


    List<Trip> tripList = new ArrayList<>();
    tripList.add(t1);
    tripList.add(t2);
    tripList.add(t3);
    tripList.add(t4);
    tripList.add(t5);

    System.out.println(Arrays.toString(tripList.toArray()));
    Collections.sort(tripList, myOrder);
    //result should be [B, A, C, D, E]
    System.out.println(Arrays.toString(tripList.toArray()));
}

}

Answer 1

写一个Comparator.

Comparator<MyType> myOrder = new Comparator<MyType>() {
    public int compare(MyType a, MyType b) {
         return (b.booleanField() ? 1 : 0) - (a.booleanField() ? 1 : 0);
    }
}

使用此比较器排序.

Collections.sort(myList, myOrder);

看到 Collections.sort

编辑

因此,您实际要求的似乎是将一个匹配元素移动到列表的前面.这应该很容易.

找到要移动的元素的索引:

int foundIndex = -1;
for (int i = 0; i < tripList.size(); ++i) {
    if (tripList.get(i).freeCancellation) {
        foundIndex = i;
        break;
    }
}

如果您找到这样的元素,并且它尚未在开头,请将其移至开头:

if (foundIndex > 0) {
    tripList.add(0, tripList.remove(foundIndex));
}