Java删库之路 support-page

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

//Iterable 迭代器  Serializable 序列化
public class Page<T> implements Iterable<T>, Serializable {
    private static final long serialVersionUID = -3720998571176536865L;//表明类的不同版本间的兼容性
    private List<T> content = new ArrayList<>();//声明和实例化ArrayList对象，并指定其类型为泛型。
    private long total;//total记录总数=pageSize*totalPages
    private int pageNo;//第几页
    private int pageSize;//页的大小，即一页能放多少数据
    private int totalPages;//总页数

    public Page() {//定义构造函数
    }

    public Page(List<T> content, long total, int pageNo, int pageSize) {
        this.content = content;
        this.total = total;
        this.pageNo = pageNo;
        this.pageSize = pageSize;
    }

    public int getTotalPages() {
        return totalPages;
    }

    public void setTotalPages(int totalPages) {
        this.totalPages = totalPages;
    }

    /**
     * Returns if there is a previous page.
     *
     * @return if there is a previous page.
     */
    public boolean hasPrevious() {//判断前一页是否存在，存在返回true，反之返回false
        return getPageNo() > 0;
    }

    /**
     * Returns if there is a next page.
     *
     * @return if there is a next page.
     */
    public boolean hasNext() {//判断后一页是否存在，存在返回true，反之返回false
        return getPageNo() + 1 < getTotalPage();
    }

    /**
     * Returns whether the current page is the first one.
     *
     * @return whether the current page is the first one.
     */
    public boolean isFirst() {//判断当前页是否是第一页
        return !hasPrevious();
    }

    /**
     * Returns whether the current  page is the last one.
     *
     * @return whether the current  page is the last one.
     */
    boolean isLast() {//判断当前页是否是最后一页
        return !hasNext();
    }

    /**
     * Returns the total amount of elements of all pages.
     *
     * @return the total amount of elements of all pages.
     */
    public long getTotal() {
        return total;
    }

    public void setTotal(long total) {
        this.total = total;
    }

    /**
     * Returns the number of total pages.
     *
     * @return the number of total pages
     */
    public int getTotalPage() {//返回总页数
        return getPageSize() == 0 ? 1 : (int) Math.ceil((double) total / (double) getPageSize());//判断页大小是否等于零，是返回总页数为一，否返回
总页数为总记录数除以页大小；ceil（）函数返回大于或等于一个给定数字的最小整数，向上取整。

    }

    /**
     * Returns the page content as unmodifiable {@link List}.
     *
     * @return Returns the page content as unmodifiable {@link List}
     */
    public List<T> getContent() {
        return Collections.unmodifiableList(content);
    }

    public void setContent(List<T> content) {
        this.content = content;
    }

    /**
     * Returns whether the current page has content.
     *
     * @return whether the current page has content.
     */
    public boolean hasContent() {//返回当前页面是否包含内容
        return getContentSize() > 0;
    }

    /**
     * Returns the number of elements on current page.
     *
     * @return the number of elements on current page.
     */
    public int getContentSize() {
        return content.size();
    }

    /**
     * Returns the number of items of each page.
     *
     * @return the number of items of each page
     */
    public int getPageSize() {
        return pageSize;
    }

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }

    /**
     * Returns the number of current page. (Zero-based numbering.)
     *
     * @return the number of current page.
     */
    public int getPageNo() {
        return pageNo;
    }

    /**
     * Set the number of current page. (Zero-based numbering.)
     */
    public void setPageNo(int pageNo) {
        this.pageNo = pageNo;
    }

    @Override
    public Iterator<T> iterator() {
        return getContent().iterator();
    }
}