A: list of use
1. Programs
package com.jun.it.java8; import java.util.ArrayList; import java.util.List; public class Foreach8 { public static void main(String[] args) { foreachList(); } //对list做foreach public static void foreachList(){ List<User> list = new ArrayList<>(); list.add(new User(1,"aaa")); list.add(new User(5,"ttt")); list.add(new User(3,"ccc")); list.forEach(user -> { user.setId(user.getId()+10); }); System.out.println(list); } private static class User{ Integer id; String name; public User(){} public User(Integer id, String name){ this.id=id; this.name=name; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "User{" + "id=" + id + ", name='" + name + '\'' + '}'; } } }
effect:
Two: Use the map
1. Programs
package com.jun.it.java8; import java.util.HashMap; import java.util.Map; public class ForeachMap { public static void main(String[] args) { foreachMap(); } //对map做foreach public static void foreachMap(){ Map<Integer,User> userMap = new HashMap<>(); userMap.put(1,new User(1,"aaa")); userMap.put(5,new User(5,"ddd")); userMap.put(3,new User(3,"ccc")); userMap.forEach((k, v)->{ System.out.println("k="+k+",v="+v); }); } private static class User{ Integer id; String name; public User(){} public User(Integer id, String name){ this.id=id; this.name=name; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "User{" + "id=" + id + ", name='" + name + '\'' + '}'; } } }
effect:
Three: Review
1. Description
Here is a description of the main previous traversal
2.entrySet method
package com.jun.it.java8; import java.util.HashMap; import java.util.Map; public class ForDemo { public static void main(String[] args) { Map<String, Integer> map = new HashMap<>(); map.put("a",1); map.put("c",3); map.put("b",2); test1(map); } //entrySet public static void test1(Map<String,Integer> map){ for (Map.Entry<String,Integer> entry : map.entrySet()){ String key = entry.getKey(); Integer value = entry.getValue(); System.out.println("key="+key+",value="+value); } } }
3.Iterator way
I found the back of the same.
package com.jun.it.java8; import java.util.HashMap; import java.util.Iterator; import java.util.Map; public class ForDemo { public static void main(String[] args) { Map<String, Integer> map = new HashMap<>(); map.put("a",1); map.put("c",3); map.put("b",2); test1(map); } //entrySet public static void test1(Map<String,Integer> map){ for (Map.Entry<String,Integer> entry : map.entrySet()){ String key = entry.getKey(); Integer value = entry.getValue(); System.out.println("key="+key+",value="+value); } } //Iterator接口 public static void test2(Map<String,Integer> map){ Iterator<Map.Entry<String, Integer>> iterator = map.entrySet().iterator(); while (iterator.hasNext()){ Map.Entry<String, Integer> next = iterator.next(); } } }
4.keySet way
package com.jun.it.java8; import java.util.HashMap; import java.util.Iterator; import java.util.Map; public class ForDemo { public static void main(String[] args) { Map<String, Integer> map = new HashMap<>(); map.put("a",1); map.put("c",3); map.put("b",2); test1(map); } //entrySet public static void test1(Map<String,Integer> map){ for (Map.Entry<String,Integer> entry : map.entrySet()){ String key = entry.getKey(); Integer value = entry.getValue(); System.out.println("key="+key+",value="+value); } } //Iterator接口 public static void test2(Map<String,Integer> map){ Iterator<Map.Entry<String, Integer>> iterator = map.entrySet().iterator(); while (iterator.hasNext()){ Map.Entry<String, Integer> next = iterator.next(); } } //使用keySet public static void test3(Map<String,Integer> map){ for (String key : map.keySet()){ Integer value=map.get(key); } } }