使用循环在 Java 中迭代列表
原文:https://www . geesforgeks . org/iterate-list-in-Java-use-loops/
在本文中，我们将看到如何遍历列表。在 Java 中，列表是集合框架的一个接口。列表可以是各种类型，如数组列表、堆栈、链接列表和向量。有多种方法可以遍历 java List，但这里我们只讨论使用循环遍历。因此，有标准的三个遍历可用，所以确实存在三个方法，但是随着 java 8 和 streams 的引入，其他方法也出现了。因此，所有四种方法讨论如下:
方法:
- 对于循环方法
- 当方法
- 对于每个循环方法
- 对于 java 8 的每个循环
实施:
方法 1: 使用 for 循环
For 循环是最常见的流量控制循环。For 循环使用一个变量来遍历列表。
例
Java 语言(一种计算机语言，尤用于创建网站)
// Java Program to Iterate List in java
// using for loop
// Importing all input output classes
import java.io.*;
// Importing all utility classes from
// java.util package
import java.util.*;
// Class
class GFG {
// main driver method
public static void main(String[] args)
{
// Creating an ArrayList object
// Declaring object of Integer type
// Custom entries in array
List<Integer> my_list
= Arrays.asList(10, 20, 30, 40, 50);
// Display message
System.out.print("Iterating over ArrayList: ");
// Iteration over ArrayList
// using the for loop
for (int i = 0; i < my_list.size(); i++)
// Print and display the all elements
// in List object
System.out.print(my_list.get(i) + " ");
// new line
System.out.println();
// No, creating a vector of size N
// Custom entry for N = 5
// Custom Integer entries
List<Integer> v = new Vector<Integer>(5);
v.add(10);
v.add(20);
v.add(30);
v.add(40);
v.add(50);
// Display message
System.out.print("Iterating over Vector: ");
// iterating over vector using for loop
for (int i = 0; i < v.size(); i++)
// Print and display vector elements
System.out.print(v.get(i) + " ");
// New Line
System.out.println();
// Creating a stack containing Integer elements
List<Integer> s = new Stack<Integer>();
// Adding integer elements
// Custom input
s.add(10);
s.add(20);
s.add(30);
s.add(40);
s.add(50);
// Display message
System.out.print("Iterating over Stack: ");
// For loop o iterate over elements in stack
for (int i = 0; i < v.size(); i++)
// Print and display all stack elements
System.out.print(s.get(i) + " ");
}
}
Output
Iterating over ArrayList: 10 20 30 40 50
Iterating over Vector: 10 20 30 40 50
Iterating over Stack: 10 20 30 40 50
方法 2: 使用 While 循环
类似于 For 循环的 Java while 循环是一个控制流语句，它允许代码重复运行，直到满足所需的条件。
例
Java 语言(一种计算机语言，尤用于创建网站)
// Java Program to iterate over List
// using while loop
// Importing all input output classes
import java.io.*;
// Importing all utility classes from
// java.util package
import java.util.*;
// Class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an object of List
// Declaring object of Integer type
// Custom Integer entries
List<Integer> my_list
= Arrays.asList(10, 20, 30, 40, 50);
// Display message
System.out.print("Iterating over ArrayList: ");
// Initially loop variable is initialized
// with zero
int i = 0;
// Iterating over List via while loop
// using size() method
while (i < my_list.size()) {
// Print and display all elements
// of an ArrayList
System.out.print(my_list.get(i) + " ");
// Incrementing the counter by unity safter
// one iteration
i++;
}
i = 0;
// New Line
System.out.println();
// Creating a Vector of size N
// Custom value for N = 5
List<Integer> v = new Vector<Integer>(5);
// Adding 5 elements to the above List object
// for vector
// Custom entries
v.add(10);
v.add(20);
v.add(30);
v.add(40);
v.add(50);
// Display message
System.out.print("Iterating over Vector: ");
// Iterating over Vector via while loop
// using the size() method
while (i < v.size()) {
// Print and display all elements of vector
System.out.print(v.get(i) + " ");
// Increment the counter variable
i++;
}
// Counter variable is initially
// initialized with zero
i = 0;
// New Line
System.out.println();
// Creating a Stack by creating another
// list object of Integer type
// Declaring object of Integer type
List<Integer> s = new Stack<Integer>();
// Adding elements to the above stack
// Custom entries
s.add(10);
s.add(20);
s.add(30);
s.add(40);
s.add(50);
// Display message
System.out.print("Iterating over Stack: ");
// Iterating over stack via while loop
// using size method()
while (i < v.size()) {
// Print and display all elements
// of the above stack/ obj created
System.out.print(s.get(i) + " ");
// Increment the counter by unity
i++;
}
}
}
Output
Iterating over ArrayList: 10 20 30 40 50
Iterating over Vector: 10 20 30 40 50
Iterating over Stack: 10 20 30 40 50
方法 3: 用于每个循环
语法:
for (type temp : list_name)
{
statements using temp;
}
例
Java 语言(一种计算机语言，尤用于创建网站)
/*package whatever //do not write package name here */
import java.io.*;
import java.util.*;
class GFG {
public static void main(String[] args)
{
// creating Arraylist
List<Integer> my_list
= Arrays.asList(10, 20, 30, 40, 50);
System.out.print("Iterating over ArrayList: ");
// For Each Loop for iterating ArrayList
for (Integer i :my_list)
System.out.print(i + " ");
System.out.println();
// creating Vector of size 5
List<Integer> v = new Vector<Integer>(5);
v.add(10);
v.add(20);
v.add(30);
v.add(40);
v.add(50);
System.out.print("Iterating over Vector: ");
// For Each Loop for iterating Vector
for (Integer i : v)
System.out.print(i + " ");
System.out.println();
// creating Stack
List<Integer> s = new Stack<Integer>();
s.add(10);
s.add(20);
s.add(30);
s.add(40);
s.add(50);
System.out.print("Iterating over Stack: ");
// For Each Loop for iterating Stack
for (Integer i : s)
System.out.print(i + " ");
}
}
Output
Iterating over ArrayList: 10 20 30 40 50
Iterating over Vector: 10 20 30 40 50
Iterating over Stack: 10 20 30 40 50
方法 4: 用于 Java 8 的每个循环
此方法将函数接口作为参数，因此 lambda 表达式可以作为参数传递。
语法:
void forEach(Consumer<? super T> action)
例
Java 语言(一种计算机语言，尤用于创建网站)
// Importing all input output classes
import java.io.*;
// Importing all classes from
// java,util package
import java.util.*;
// Class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an Arraylist by creating object
// of List and declaring as Integer type
// Custom Integer entries
List<Integer> my_list
= Arrays.asList(10, 20, 30, 40, 50);
// Display message
System.out.print("Iterating over ArrayList: ");
// Traversing over ArrayList
// using for each method Java 8
my_list.forEach(
list -> System.out.print(list + " "));
// New line
System.out.println();
// creating Vector by creating object of
// List and declaring as Integer type
// Vector is of size N
// N = 5 for illustration purposes
List<Integer> v = new Vector<Integer>(5);
// Adding elements to the vector
// Custom Integer elements
v.add(10);
v.add(20);
v.add(30);
v.add(40);
v.add(50);
// Display message
System.out.print("Iterating over Vector: ");
// Traversing the above vector elements
// using for each method Java 8
v.forEach(vector -> System.out.print(vector + " "));
// New line
System.out.println();
// Creating a Stack by creating an object of
// List and declaring it as of Integer type
List<Integer> s = new Stack<Integer>();
// Adding elements to the above stack created
// Custom inputs addition using add() method
s.add(10);
s.add(20);
s.add(30);
s.add(40);
s.add(50);
// Display message
System.out.print("Iterating over Stack: ");
// Print and display all the elements inside stack
// using for each method Java 8
s.forEach(stack -> System.out.print(stack + " "));
}
}
Output
Iterating over ArrayList: 10 20 30 40 50
Iterating over Vector: 10 20 30 40 50
Iterating over Stack: 10 20 30 40 50
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