Java Tutorial/Statement Control/For Each Loop
Содержание
- 1 Iterating over Multidimensional Arrays: Use for-each style for on a two-dimensional array
- 2 The for each loop for an enum data type
- 3 The for-each loop is essentially read-only
- 4 The For-Each Version of the for Loop
- 5 Use a for-each style for loop
- 6 Using break with a for-each-style for
- 7 Using "for each" to loop through array
- 8 Using the For-Each Loop with Collections: ArrayList
Iterating over Multidimensional Arrays: Use for-each style for on a two-dimensional array
<source lang="java">
public class MainClass {
public static void main(String args[]) {
int sum = 0;
int nums[][] = new int[3][5];
// give nums some values
for (int i = 0; i < 3; i++)
for (int j = 0; j < 5; j++)
nums[i][j] = (i + 1) * (j + 1);
// use for-each for to display and sum the values
for (int x[] : nums) {
for (int y : x) {
System.out.println("Value is: " + y);
sum += y;
}
}
System.out.println("Summation: " + sum);
}
}</source>
Value is: 1 Value is: 2 Value is: 3 Value is: 4 Value is: 5 Value is: 2 Value is: 4 Value is: 6 Value is: 8 Value is: 10 Value is: 3 Value is: 6 Value is: 9 Value is: 12 Value is: 15 Summation: 90
The for each loop for an enum data type
<source lang="java">
for (type identifier : iterable_expression) {
// statements
}</source>
The season is now spring The season is now summer The season is now fall The season is now winter
The for-each loop is essentially read-only
<source lang="java">
public class MainClass {
public static void main(String args[]) {
int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
for(int x : nums) {
System.out.print(x + " ");
x = x * 10; // no effect on nums
}
System.out.println();
for(int x : nums)
System.out.print(x + " ");
System.out.println();
}
}</source>
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10
The For-Each Version of the for Loop
The general form of the for-each version of the for is shown here:
<source lang="java">
for(type itr-var : iterableObj) statement-block</source>
The object referred to by iterableObj must be an array or an object that implements the new Iterable interface.
Use a for-each style for loop
<source lang="java">
public class MainClass {
public static void main(String args[]) {
int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int sum = 0;
// use for-each style for to display and sum the values
for(int x : nums) {
System.out.println("Value is: " + x);
sum += x;
}
System.out.println("Summation: " + sum);
}
}</source>
Value is: 1 Value is: 2 Value is: 3 Value is: 4 Value is: 5 Value is: 6 Value is: 7 Value is: 8 Value is: 9 Value is: 10 Summation: 55
Using break with a for-each-style for
<source lang="java">
public class MainClass {
public static void main(String args[]) {
int sum = 0;
int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
// Use for to display and sum the values.
for (int x : nums) {
System.out.println("Value is: " + x);
sum += x;
if (x == 5){
break; // stop the loop when 5 is obtained
}
}
System.out.println("Summation of first 5 elements: " + sum);
}
}</source>
Value is: 1 Value is: 2 Value is: 3 Value is: 4 Value is: 5 Summation of first 5 elements: 15
Using "for each" to loop through array
<source lang="java">
public class MainClass {
public static void main(String[] arg) {
char[] vowels = { "a", "e", "i", "o", "u"};
for(char ch: vowels){
System.out.println(ch);
}
}
}</source>
a e i o u
Using the For-Each Loop with Collections: ArrayList
For-Each Loop can be used to any object that implements the Iterable interface. This includes all collections defined by the Collections Framework,
<source lang="java">
import java.util.ArrayList;
public class MainClass {
public static void main(String args[]) {
ArrayList<Double> list = new ArrayList<Double>();
list.add(10.14);
list.add(20.22);
list.add(30.78);
list.add(40.46);
double sum = 0.0;
for(double itr : list)
sum = sum + itr;
System.out.println(sum);
}
}</source>
101.6
