Question

我需要编写一个Java程序（类LinkedList-Queue），它应该在不使用导入列表的情况下执行所有操作，我已经尝试但是我无法创建推送方法而且需要帮助。

有人可以帮帮我吗？你可以在我的github帐户中找到我的所有课程： https://github.com/mertowski/Fortgeschrittene-Programmierung/tree/master/012.%20Aufgabe%204%20Generische%20Queue

这是我的班级：

package main.java.a4;
//First In First Out
public class Queue<K> {

    QueueNode first;
    QueueNode last;
    private int size = 0;

    //-------------------Innere Klasse------------------------------
        private class QueueNode {
            K data;
            QueueNode next;
            public QueueNode(K data, QueueNode next) {
                this.data = data;
                this.next = next;
            }

            public void setData() {
                this.data = data;
            }

            public void setNext() {
                this.next = next;
            }
        }
    //-------------------Innere Klasse------------------------------


    //(Methode zum Einfügen eines Elements in die Queue)
    public void push(K element) {
        if(element == null) {
            throw new NullPointerException("Element was null!");
        }
        if(first == null) {
            //here
        } else {
            //and here
        }
    } 

    //(Methode zum herausnehmen eines Elements aus der Warteschlange)
    public K pull() {
        if (first == null) {
            throw new NullPointerException("Queue was empty!");
        } else {
            QueueNode temp = first;
            first = first.next;
            if(size == 1) {
                last = null;
            }
            size--;
            return temp.data;
        }
    } 

//(Gibt die Anzahl der in der Liste gespeicherten Elemente zurück)
public int size() {
    return size;
} 

public String toString() {
    QueueNode temp = first;
    StringBuilder sb = new StringBuilder();
    while (temp != null) {
        sb.append("<" + temp.data + ">");
        temp = temp.next;
    }
    return sb.toString();
}

public boolean isEmpty() {
    if(first == null) {
        return true;
    } else {
        return false;
    }
}

}

这是我的测试类J-Unit：

package test.java.a4;


import main.java.a4.Account;
import main.java.a4.AccountDetails;
import main.java.a4.Euro;
import main.java.a4.Queue;
import main.java.a4.Transaction;
import org.junit.Before;
import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class QueueTest {

    private Queue<Transaction> transactions;
    private Transaction transaction1;
    private Transaction transaction2;
    private Transaction transaction3;

    //Method is called before every test method.
    @Before
    public void setUp() {
        this.transactions = new Queue<>();
        Account<Euro> acc1 = new Account<>(new AccountDetails("10001", "Bank1"), 20000d, 50000d, new Euro(1, "EUR"), 123);
        this.transaction1 = new Transaction(acc1, "10002", 20000);
        Account<Euro> acc2 = new Account<>(new AccountDetails("10002", "Bank1"), 20000d, 50000d, new Euro(1, "EUR"), 123);
        this.transaction2 = new Transaction(acc2, "10001", 30000);
        Account<Euro> acc3 = new Account<>(new AccountDetails("10004", "Bank1"), 20000d, 50000d, new Euro(1, "EUR"), 123);
        this.transaction3 = new Transaction(acc3, "10006", 50000);
    }

    //try to push null
    @Test(expected = NullPointerException.class)
    public void testPushNullElement() {
        this.transactions.push(null);
    }

    //test if the queue is empty
    @Test
    public void testQueueIsEmpty() {
        assertEquals(true, transactions.isEmpty());
    }

    //test if the size is zero when the queue is empty
    @Test
    public void testQueueSizeZero() {
        assertEquals(0, transactions.size());
    }

    //try to push one element
    @Test
    public void testPushFirstElement() {
        transactions.push(transaction1);
        assertEquals("<10002>", transactions.toString());
    }

    //test if the size is one after an element was pushed
    @Test
    public void testQueueSizeOne() {
        transactions.push(transaction1);
        assertEquals(1, transactions.size());
    }

    //try to push two elements
    @Test
    public void testPushSecondElement() {
        transactions.push(transaction1);
        this.transactions.push(transaction2);
        assertEquals("<10002><10001>", this.transactions.toString());
    }

    //test if the size is two after two elements were pushed
    @Test
    public void testQueueSizeTwo() {
        transactions.push(transaction1);
        transactions.push(transaction2);
        assertEquals(2, transactions.size());
    }

    //try to push three elements
    @Test
    public void testPushThirdElement() {
        transactions.push(transaction1);
        transactions.push(transaction2);
        transactions.push(transaction3);
        assertEquals("<10002><10001><10006>", this.transactions.toString());
    }

    //test if the size is three after three elements were pushed
    @Test
    public void testQueueSizeThree() {
        transactions.push(transaction1);
        transactions.push(transaction2);
        transactions.push(transaction3);
        assertEquals(3, transactions.size());
    }

    //add three elements and try to pull the first one
    @Test
    public void testQueuePullFirstTransaction() {
        transactions.push(transaction1);
        transactions.push(transaction2);
        transactions.push(transaction3);
        assertEquals(transaction1.getTargetIban(), transactions.pull().getTargetIban());
    }

    //add two elements and try to pull the first one
    @Test
    public void testQueuePullSecondTransaction() {
        transactions.push(transaction2);
        transactions.push(transaction3);
        assertEquals(transaction2.getTargetIban(), transactions.pull().getTargetIban());
    }

    //add one element and try to pull it
    @Test
    public void testQueuePullThirdTransaction() {
        transactions.push(transaction3);
        assertEquals(transaction3.getTargetIban(), transactions.pull().getTargetIban());
    }
}

Answer 1

此代码应该这样做

public void push(K element) {
    if (element == null) {
        throw new NullPointerException("Element was null!");
    }
    QueueNode newNode = new QueueNode(element, first);
    if (first == null) {
        last = newNode;
    }
    first = newNode;
}

LinkedList Queue推送方法，使用内核类QueueNode

1 个答案: