集合實例練習
a:自然排序
測試類：
`package treeSet集合;
import java.util.Comparator;
import java.util.Scanner;
import java.util.TreeSet;
public class ZuoyeScannerSelect {
public static void main(String[] args) {
TreeSet<StudentSelect> ts=new TreeSet<StudentSelect>(new Comparator<StudentSelect>() {
@Override public int compare(StudentSelect s1, StudentSelect s2) { int num1=s2.sum(s2)-s1.sum(s1); int num2=(num1==0)?s2.getName().compareTo(s1.getName()):num1; return num2; } }) ; System.out.println("請輸入學生信息:"); //錄入學生信息 for(int x=1;x<6;x++) { Scanner sc=new Scanner(System.in); System.out.print("請輸入第"+x+"個學生的姓名:"); //錄入學生姓名 String name=sc.nextLine(); System.out.print("請輸入第"+x+"個學生的語文成績:"); //錄入學生語文成績 int chineseScore=sc.nextInt(); System.out.print("請輸入第"+x+"個學生的數學成績:"); //錄入學生數學成績 int mathScore=sc.nextInt(); System.out.print("請輸入第"+x+"個學生的英語成績:"); //錄入學生英語成績 int englishScore=sc.nextInt(); //將學生信息封裝到學生對象裏 StudentSelect s=new StudentSelect(); s.setName(name); s.setChineseScore(chineseScore); s.setMathScore(mathScore); s.setEnglishScore(englishScore); //把學生對象添加到集合中 ts.add(s); } //遍歷 for(StudentSelect s:ts) { System.out.println(s.getName()+","+ + s.getChineseScore()+"," + s.getMathScore()+","+ s.getEnglishScore()+","+s.sum(s)); } }
}`
實體類：
package treeSet集合; public class StudentZiran implements Comparable<StudentZiran>{ //自然排序,自定義類中實現Comparable接口 private String name; private int chineseScore; private int mathScore; private int englishScore; public StudentZiran() {//無參構造 // TODO Auto-generated constructor stub } //有參構造 public StudentZiran(String name,int chineseScore,int mathScore,int englishScore) { this.name=name; this.chineseScore=chineseScore; this.mathScore=mathScore; this.englishScore=englishScore; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getChineseScore() { return chineseScore; } public void setChineseScore(int chineseScore) { this.chineseScore = chineseScore; } public int getMathScore() { return mathScore; } public void setMathScore(int mathScore) { this.mathScore = mathScore; } public int getEnglishScore() { return englishScore; } public void setEnglishScore(int englishScore) { this.englishScore = englishScore; } //求總成績方法 public int sum(StudentZiran s) { return s.getChineseScore()+s.getMathScore()+s.getEnglishScore(); } //重寫compearTo()方法 @Override public int compareTo(StudentZiran s) { //主要排序條件:總成績,按總成績從高到低 int num1=s.sum(s)-this.sum(this); //次要排序條件,當總成績相同時按學生姓名內容比較 int num2=(num1==0)?s.getName().compareTo(this.getName()):num1; return num2; } }
b:選擇器排序
測試類：
`package treeSet集合;import java.util.Comparator;
import java.util.Scanner;
import java.util.TreeSet;
public class ZuoyeScannerSelect {
public static void main(String[] args) {
TreeSet<StudentSelect> ts=new TreeSet<StudentSelect>(new Comparator<StudentSelect>() {
@Override
public int compare(StudentSelect s1, StudentSelect s2) {
int num1=s2.sum(s2)-s1.sum(s1);
int num2=(num1==0)?s2.getName().compareTo(s1.getName()):num1;
return num2;
}
}) ;
System.out.println("請輸入學生信息:");
//錄入學生信息
for(int x=1;x<6;x++) {
Scanner sc=new Scanner(System.in);
System.out.print("請輸入第"+x+"個學生的姓名:");
//錄入學生姓名
String name=sc.nextLine();
System.out.print("請輸入第"+x+"個學生的語文成績:");
//錄入學生語文成績
int chineseScore=sc.nextInt();
System.out.print("請輸入第"+x+"個學生的數學成績:");
//錄入學生數學成績
int mathScore=sc.nextInt();
System.out.print("請輸入第"+x+"個學生的英語成績:");
//錄入學生英語成績
int englishScore=sc.nextInt();
//將學生信息封裝到學生對象裏
StudentSelect s=new StudentSelect();
s.setName(name);
s.setChineseScore(chineseScore);
s.setMathScore(mathScore);
s.setEnglishScore(englishScore);
//把學生對象添加到集合中
ts.add(s);
}
//遍歷
for(StudentSelect s:ts) {
System.out.println(s.getName()+","+ + s.getChineseScore()+","
+ s.getMathScore()+","+ s.getEnglishScore()+","+s.sum(s));
}
} }`
實體類：
package treeSet集合;
public class StudentSelect {
private String name;
private int chineseScore;
private int mathScore;
private int englishScore;
public StudentSelect() {//無參構造
// TODO Auto-generated constructor stub
}
//有參構造
public StudentSelect(String name,int chineseScore,int mathScore,int englishScore) {
this.name=name;
this.chineseScore=chineseScore;
this.mathScore=mathScore;
this.englishScore=englishScore;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getChineseScore() {
return chineseScore;
}
public void setChineseScore(int chineseScore) {
this.chineseScore = chineseScore;
}
public int getMathScore() {
return mathScore;
}
public void setMathScore(int mathScore) {
this.mathScore = mathScore;
}
public int getEnglishScore() {
return englishScore;
}
public void setEnglishScore(int englishScore) {
this.englishScore = englishScore;
}
//求總成績方法
public static int sum(StudentSelect s) {
return s.getChineseScore()+s.getMathScore()+s.getEnglishScore();
}
}2、獲取10隨機數,1-20之間,要求值不能重復!(ArrayList,HashSet)
ArrayList：
package 集合獲取隨機數;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Random;
public class ArrayListGetRandom {
public static void main(String[] args) {
//創建集合al
ArrayList<Integer> al=new ArrayList<Integer>();
//創建新集合newal
ArrayList<Integer> newal=new ArrayList<Integer>();
//判斷新集合newal中的元素個數是否夠10個,若不夠,繼續添加
while(newal.size()<10) {
//創建獲取隨機數對象
Random r=new Random();
//獲取隨機數
int n=r.nextInt(20);
//將獲取到的隨機數添加到集合al集合
al.add(n);
//遍歷舊集合
Iterator<Integer> it=al.iterator();
while(it.hasNext()) {
int i=it.next();
//判斷newal中是否包含al中的元素,若不包含,將al中的元素添加到newal中
if(!newal.contains(i)) {
newal.add(i);
}
}
//遍歷newal集合
for(int i:newal) {
System.out.println(i);
}
}
}
}
HashSet：
package 集合獲取隨機數;
import java.util.HashSet;
import java.util.Random;
import java.util.Set;
public class HashSetGetRandom {
public static void main(String[] args) {
//創建Set集合對象
Set<Integer> set=new HashSet<Integer>();
//創建獲取隨機數類對象
Random r=new Random();
//判斷已獲取隨機數個數,若不夠10個,則繼續添加
while(set.size()<10) {
//獲取隨機數
int n=r.nextInt(20);
//將獲取的隨機數添加到集合set中
set.add(n);
}
//增強for循環遍歷集合set
for(int i:set) {
System.out.println(i);
}
}
}3、ArrayList集合嵌套HashMap集合並遍歷。
需求：
假設ArrayList集合的元素是HashMap。有3個。
每一個HashMap集合的鍵和值都是字符串。
元素如下，請遍歷。
ArrayList<HashMap<String,String>>
結果：
周瑜---小喬
呂布---貂蟬
郭靖---黃蓉
楊過---小龍女
令狐沖---任盈盈
林平之---嶽靈珊
`package 集合嵌套;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Set;
public class AM {
public static void main(String[] args) {
//創建一個大的ArrayList集合am
ArrayList<HashMap<String,String>> am=new ArrayList<HashMap<String,String>>();
//創建第一個HashMap集合hm1
HashMap<String,String> hm1=new HashMap<String,String>();
//給集合hm1添加元素
hm1.put("周瑜","小喬");
hm1.put("呂布","貂蟬");
//將hm1的元素添加到大集合am中
am.add(hm1);
//創建第二個HashMap集合hm2
HashMap<String,String> hm2=new HashMap<String,String>();
//給集合hm2添加元素
hm2.put("郭靖","黃蓉");
hm2.put("楊過","小龍女");
//將hm2的元素添加到大集合am中
am.add(hm2);
//創建第三個HashMap集合hm3
HashMap<String,String> hm3=new HashMap<String,String>();
//給集合hm3添加元素
hm3.put("令狐沖","任盈盈");
hm3.put("林平之","嶽靈珊");
//將hm3的元素添加到大集合am中
am.add(hm3);
//遍歷大集合am
for(HashMap<String,String> ahm:am) {
Set<String> set=ahm.keySet();
for(String key:set) {
String value=ahm.get(key);
System.out.println(key+"---"+value);
}
System.out.println();
}
}
}`
集合實例練習