はじめに#

JavaとPythonの基礎文法を比較してみました。
Javaの文法が汚かったり、違う部分があればご指摘いただけるとありがたいです！

目次#

1.出力
 2.変数
 3.文字列と数値の結合
 4.if文
 5.for文
 6.while文
 7.forとwhileでbreak, continue
8.list
9.辞書

1.出力#

python

print('123')
print(123)
>>>123
>>>123

java

public class Main {
    public static void main(String[] args){
        
        System.out.println("123");
        System.out.println(123);
    }
}
>>>123
>>>123

2.変数#

python

mystr = 'hello'
myint = 123
print(mystr)
print(myint)
>>>hello
>>>123

java

public class Main {
    public static void main(String[] args){
        
        String mystr = "hello";
        int myint = 123;
        
        System.out.println(mystr);
        System.out.println(myint);
    }
}
>>>hello
>>>123

3.文字列と数値の結合#

python

myint = 123
print('数字は' + str(myint))
>>>数字は123

java

public class Main {
    public static void main(String[] args){
        
        int myint = 123;
        System.out.println("数字は" + myint);
    }
}
>>>数字は123

4.if文#

python

myint = 10
if myint == 10:
    print('myintは10です')
>>>myintは10です

java

public class Main {
    public static void main(String[] args){
        
        int myint = 10;
        if(myint == 10){
            System.out.println("myintは10です");
        }
    }
}
>>>myintは10です

5.for文#

python

for char in 'Hello':
    print(char)
>>>H
>>>e
>>>l
>>>l
>>>o

java

//splitと拡張for文
public class Main {
    public static void main(String[] args){
        
        String mystr = "hello";
        String[] strArray = mystr.split("");
        for(String s : strArray) {
	        System.out.println(s);
            }
    }
}

//charAtとfor文
public class Main {
    public static void main(String[] args){
        
        String mystr = "hello";
        for(int i = 0; i < mystr.length(); i++) {
	        System.out.println(mystr.charAt(i));
            }
    }
}

>>>h
>>>e
>>>l
>>>l
>>>o

・指定回数だけループ###

python

for i in range(3):
    print(i)
>>>0
>>>1
>>>2

java

public class Main {
    public static void main(String[] args){
        
    for(int i = 0; i < 3; i++) {
        System.out.println(i);
        }
    }
}
>>>0
>>>1
>>>2

・リスト、配列のループ処理###

python

list = ['item1', 'item2', 'item3']
for item in list:
    print(item)
>>>item1
>>>item2
>>>item3

java

public class Main {
    public static void main(String[] args){
        
        String[] list = {"item1", "item2", "item3"};
        for(int i = 0; i <list.length; i++){
            System.out.println(list[i]);
        }
    }
}
>>>item1
>>>item2
>>>item3

6.While文#

python

val = 0
while val < 4:
    val += 1
    print(val)
print('valは' + str(val))
>>>1
>>>2
>>>3
>>>4
>>>valは4

java

public class Main {
    public static void main(String[] args){
        
        int val = 0;
        while(val < 4){
            val++;
            System.out.println(val);
        }
        System.out.println("valは" + val);
    }
}
>>>1
>>>2
>>>3
>>>4
>>>valは4

7.forとwhileでbreak, continue

・for文でbreak###

python

list = [1,2,3,4,5]
for i in list:
    if i == 3:
        break
    print(i)
>>>1
>>>2
>>>breakで繰り返し処理終了

java

public class Main {
    public static void main(String[] args){
        
        int[] list = {1,2,3,4,5};
        for(int i = 1; i < list.length; i++){
            if(i == 3){
                break;
            }
            System.out.println(i);
        }
    }
}
>>>1
>>>2
>>>breakで繰り返し処理終了

・while文でbreak###

python

val = 1 
while val < 10:
    if val == 3:
        break 
    print(val)
    val += 1
>>>1
>>>2
>>>breakで繰り返し処理終了

java

public class Main {
    public static void main(String[] args){
        
        int val = 1;
        while(val < 10){
            if(val == 3){
                break;
            }
            System.out.println(val);
            val++;
        }
    }
}
>>>1
>>>2
>>>breakで繰り返し処理終了

・for文でcontinue###

python

# for文でcontinue
list = [1,2,3,4,5]
for i in list:
    if i == 2:
        continue
    print(i)
>>>1
>>>3
>>>4
>>>5

java

public class Main {
    public static void main(String[] args){
        
        int[] list = {1,2,3,4,5};
        for(int i = 1; i < list.length+1; i++){
            if(i == 2){
                continue;
            }
            System.out.println(i);
        }
    }
}
>>>1
>>>3
>>>4
>>>5

・while文でcontinue###

python

val = 0
while val < 5:
    val += 1
    if val == 2:
        continue
    print(val)
>>>1
>>>3
>>>4
>>>5

java

public class Main {
    public static void main(String[] args){
        
        int val = 1;
        while(val < 6){
            if(val == 2){
                val++;
                continue;
            }
            System.out.println(val);
            val++;
        }
    }
}
>>>1
>>>3
>>>4
>>>5

8.list#

pythonではリストが配列の役割を担っています。

python

list = ['a','b','c']
print(list)
>>>['a','b','c']

Javaではリストの中身を全部一気に取得できないので、forを使って一つずつ呼び出す必要があります。

java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args){
        
        List<String> list = new ArrayList<String>(Arrays.asList("a", "b", "c"));
        
        for(int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
    }
}
>>>a
>>>b
>>>c

・リスト内の要素の参照###

python

list = ['a','b','c']
# 先頭の要素
print(list[0])
# ２番目の要素
print(list[2])
>>>a
>>>c

java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args){
        
        List<String> list = new ArrayList<String>(Arrays.asList("a", "b", "c"));
        //先頭の要素
        System.out.println(list.get(0));
        //２番目の要素
        System.out.println(list.get(2));
    }
}
>>>a
>>>c

・リストへの値の追加###

python

list = ['a','b','c']
# 末尾に追加
list.append('d')
# 指定位置に追加
list.insert(2, 'd')

print(list)
>>>['a','b','d','c','d']

java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args){

        List<String> list = new ArrayList<String>(Arrays.asList("a", "b", "c"));
        //末尾に追加
        list.add("d");
        //指定位置に追加
        list.add(2, "d");
    }
}
>>>{"a","b","d","c","d"}

・リストからの値の削除###

python

list = ['a','b','c']
# 末尾の要素を削除
list.pop()
# 指定位置の要素を削除
list.pop(1)
print(list)

>>>['a']

java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args){

        List<String> list = new ArrayList<String>(Arrays.asList("a", "b", "c"));
        //指定位置の要素を削除
        list.remove(0);
    }
}
>>>{"b","c"}

・リストの値の更新###

python

list = ['a','b','c']
list[1] = 'x'
print(list)
>>>['a','x','c']

java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args){

        List<String> list = new ArrayList<String>(Arrays.asList("a", "b", "c"));
        list.set(1,"x");
    }
}
>>>{"a","x","c"}

9.辞書、Map#

python

dict = { 'apple':1, 'orange':2, 'banana':3 }
print(dict['apple'])
>>>1

java

import java.util.LinkedHashMap;

public class Main {
    public static void main(String[] args){

        LinkedHashMap<String, Integer> map = new LinkedHashMap<>() ;
            
        map.put("apple", 1);
        map.put("orange", 2);
        map.put("banana", 3);
            
        System.out.println(map);
        System.out.println(map.get("apple"));
    }
}
>>>{apple=1, orange=2, banana=3}
>>>1

順序を保持して入れたかったので今回はLinkedHashMapを使いました。

Mapの種類と特徴
LinkedHashMap:
キーを格納した順に保持。
TreeMap:
キーの昇順に保持。
HashMap:
順序を保持しない。

・辞書、Mapの値の更新###

python

dict = { 'apple':1, 'orange':2, 'banana':3 }
dict['apple'] = 5
print(dict)
>>>{ 'apple':5, 'orange':2, 'banana':3 }

java

import java.util.LinkedHashMap;

public class Main {
    public static void main(String[] args){

        LinkedHashMap<String, Integer> map = new LinkedHashMap<>() ;
            
        map.put("apple", 1);
        map.put("orange", 2);
        map.put("banana", 3);
        
        map.put("apple",5);
        System.out.println(map);
    }
}
>>>{apple=5, orange=2, banana=3}

・辞書、Mapの値の削除###

python

dict = { 'apple':1, 'orange':2, 'banana':3 }
del dict['apple'] 
print(dict)
>>>{'orange':2, 'banana':3 }

java

import java.util.LinkedHashMap;

public class Main {
    public static void main(String[] args){

        LinkedHashMap<String, Integer> map = new LinkedHashMap<>() ;
            
        map.put("apple", 1);
        map.put("orange", 2);
        map.put("banana", 3);
        
        map.remove("apple");
        System.out.println(map);
    }
}
>>>{orange=2, banana=3}

・キーの存在確認###

python

dict = { 'apple':1, 'orange':2, 'banana':3 }
if 'apple' in dict:
    print('存在します')
else:
    print('存在しません')
>>>存在します

java

import java.util.LinkedHashMap;

public class Main {
    public static void main(String[] args){

        LinkedHashMap<String, Integer> map = new LinkedHashMap<>() ;
            
        map.put("apple", 1);
        map.put("orange", 2);
        map.put("banana", 3);
        
        if(map.containsKey("apple")){
            System.out.println("存在します");
        }else{
            System.out.println("存在しません");
        }
    }
}
>>>存在します