Don't think that you can always get the idea if you know Japanese and you read Chinese Handzi.
One example is, that 新聞(しんぶん)which is Japanese for Newspaper, in Chinese means Toilette Paper.
So be careful, because as this example there might be a lot, I guess.
Correct me if I am wrong.
Santi
I am sure you mean "letter" (Japanese: 手紙 (tegami) - letter, Mandarin: 手纸 (simplified) / 手紙 (traditional) shǒuzhǐ - toilet paper), not newspaper 新聞 - shinbun, in Mandarin 新闻 (simplified) / 新聞 (traditional) xīnwén means "news".
As for the simplified/traditional. Japanese have also simplified a lot of characters, about 30% of characters that were simplified on the Mainland. Below are some examples where Japanese modern characters match Mainland's simplified. On the right side I put the traditional, more complex form.
国 國
会 會
点 點
万 萬
声 聲
医 醫
写 寫
湾 灣
号 號
There's a number of characters where Japanese simplified them but differently from mainland China. These characters now have at least 3 versions: Japanese simplified (modern standard), Chinese simplified and Chinese traditional.
Here are some examples of those:
Japanese, Chinese (simplified), Chinese (traditional)
気 气 氣
楽 乐 樂
帰 归 歸
専 专 專
満 满 滿
図 图 圖
録 录 錄
処 处 處
黒 黑 黑
戸 户 戶
単 单 單
捜 搜 搜
従 从 從
雑 杂 雜
Learned words, usually nouns very often match in both Chinese and Japanese, sometimes you need to take into account simplification and variants to find that match. Both languages are very different in grammar, word order and pronunciation. As S_a_n_t_i mentioned, you can't rely 100% on the match too, even if you recognise the characters, alos usage and importance differs. A common character in one language might be an ancient or hardly used in another. To read Japanese texts, you need to know 2 syllabaries (46 in each) + about 2,000+ characters. You are efficient in Chinese if you master 3,500 - 4,000 characters. (Of course, learning Chinese or Japanese is not just learning the characters but words, combinations, grammar, pronunciations, usage, etc.)
電話 denwa telephone (Japanese); 电话 / 電話 diànhuà telephone (Mandarin)
政治 seiji politics (Japanese); 政治 zhèngzhì politics (Mandarin)
漢字 kanji Chinese character (Japanese); 汉字 /漢字 hànzì Chinese character (Mandarin)
Japanese has borrowed a lot of words from European languages, which are written in katakana - one of the 2 Japanese alphabets. A normal Japanese text consists of both kanji and hiragana or katakana. Hiragana is used to write endings, grammatical forms, some other words, katakana is used to write foreign words, names of animals, onomatopoeia, etc. Chinese write everything in hanzi (Chinese characters), including all foreign words, the number of loanwords is much smaller in Chinese dialects and Mandarin.
P.S. Pity, there's no Chinese forum here.