• Java 打印模板
下面这份够覆盖刷题和面试里大多数场景。
import java.util.*;
public class PrintTemplates {
// 链表节点
static class ListNode {
int val;
ListNode next;
ListNode(int val) { this.val = val; }
}
// 二叉树节点
static class TreeNode {
int val;
TreeNode left, right;
TreeNode(int val) { this.val = val; }
}
// 自定义对象
static class User {
String name;
int age;
User(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public String toString() {
return "User{name='" + name + "', age=" + age + "}";
}
}
public static void main(String[] args) {
// 1. 基本类型 / 字符串
int x = 10;
String s = "hello";
System.out.println(x);
System.out.println(s);
// 2. 一维数组
int[] arr = {1, 2, 3, 4};
System.out.println(Arrays.toString(arr));
// 3. 二维数组
int[][] matrix = {{1, 2}, {3, 4}, {5, 6}};
System.out.println(Arrays.deepToString(matrix));
// 4. 一行一行打印二维数组
for (int[] row : matrix) {
System.out.println(Arrays.toString(row));
}
// 5. List
List<Integer> list = Arrays.asList(1, 2, 3);
System.out.println(list);
// 6. Set
Set<String> set = new HashSet<>(Arrays.asList("a", "b", "c"));
System.out.println(set);
// 7. Map
Map<String, Integer> map = new HashMap<>();
map.put("Alice", 18);
map.put("Bob", 20);
System.out.println(map);
// 8. 自定义对象
User user = new User("Tom", 22);
System.out.println(user);
// 9. 对象数组 / 对象集合
User[] users = {new User("A", 10), new User("B", 20)};
System.out.println(Arrays.toString(users));
System.out.println(Arrays.asList(users));
// 10. 链表
ListNode head = new ListNode(1);
head.next = new ListNode(2);
head.next.next = new ListNode(3);
printList(head);
// 11. 二叉树
TreeNode root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
root.left.right = new TreeNode(4);
System.out.print("前序: ");
preorder(root);
System.out.println();
System.out.print("中序: ");
inorder(root);
System.out.println();
System.out.print("后序: ");
postorder(root);
System.out.println();
System.out.print("层序: ");
levelOrder(root);
System.out.println();
// 12. 格式化输出
System.out.printf("name=%s, age=%d%n", "Jerry", 18);
}
// 打印链表
public static void printList(ListNode head) {
while (head != null) {
System.out.print(head.val);
if (head.next != null) {
System.out.print(" -> ");
}
head = head.next;
}
System.out.println();
}
// 前序遍历
public static void preorder(TreeNode root) {
if (root == null) return;
System.out.print(root.val + " ");
preorder(root.left);
preorder(root.right);
}
// 中序遍历
public static void inorder(TreeNode root) {
if (root == null) return;
inorder(root.left);
System.out.print(root.val + " ");
inorder(root.right);
}
// 后序遍历
public static void postorder(TreeNode root) {
postorder(root.right);
System.out.print(root.val + " ");
}
// 层序遍历
public static void levelOrder(TreeNode root) {
if (root == null) return;
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()) {
TreeNode node = queue.poll();
System.out.print(node.val + " ");
if (node.left != null) queue.offer(node.left);
if (node.right != null) queue.offer(node.right);
}
}
}
最常用速记版
-
一维数组：Arrays.toString(arr)
-
二维数组：Arrays.deepToString(arr)
-
集合：System.out.println(list)
-
Map：System.out.println(map)
-
链表：while 遍历打印
-
二叉树：前序 / 中序 / 后序 / 层序
-
自定义对象：重写 toString()
补充
如果你刷 LeetCode，最实用的是这几个：
System.out.println(Arrays.toString(arr));
System.out.println(Arrays.deepToString(matrix));
System.out.println(list);
System.out.println(map);
printList(head);
levelOrder(root);