JRE 8 rt.jar is the JAR file for JRE 8 RT (Runtime) libraries. JRE (Java Runtime) 8 is the runtime environment included in JDK 8. JRE 8 rt.jar libraries are divided into 6 packages:

com.* - Internal Oracle and Sun Microsystems libraries
java.* - Standard Java API libraries.
javax.* - Extended Java API libraries.
jdk.* -  JDK supporting libraries.
org.* - Third party libraries.
sun.* - Old libraries developed by Sun Microsystems.

JAR File Information:

Directory of C:\fyicenter\jdk-1.8.0_191\jre\lib
      63,596,151 rt.jar

Here is the list of Java classes of the com.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ com/sun/java/swing/plaf/motif/resources/motif_ja.java

package com.sun.java.swing.plaf.motif.resources;

import java.util.ListResourceBundle;

public final class motif_ja extends ListResourceBundle {
    protected final Object[][] getContents() {
        return new Object[][] {
            { "FileChooser.acceptAllFileFilter.textAndMnemonic", "*" },
            { "FileChooser.cancelButton.textAndMnemonic", "\u53D6\u6D88" },
            { "FileChooser.cancelButtonToolTip.textAndMnemonic", "\u30D5\u30A1\u30A4\u30EB\u30FB\u30C1\u30E5\u30FC\u30B6\u30FB\u30C0\u30A4\u30A2\u30ED\u30B0\u3092\u7D42\u4E86\u3057\u307E\u3059\u3002" },
            { "FileChooser.enterFileNameLabel.textAndMnemonic", "\u30D5\u30A1\u30A4\u30EB\u540D\u3092\u5165\u529B(&N):" },
            { "FileChooser.enterFolderNameLabel.textAndMnemonic", "\u30D5\u30A9\u30EB\u30C0\u540D\u3092\u5165\u529B:" },
            { "FileChooser.filesLabel.textAndMnemonic", "\u30D5\u30A1\u30A4\u30EB(&I)" },
            { "FileChooser.filterLabel.textAndMnemonic", "\u30D5\u30A3\u30EB\u30BF(&R)" },
            { "FileChooser.foldersLabel.textAndMnemonic", "\u30D5\u30A9\u30EB\u30C0(&L)" },
            { "FileChooser.helpButton.textAndMnemonic", "\u30D8\u30EB\u30D7" },
            { "FileChooser.helpButtonToolTip.textAndMnemonic", "FileChooser\u306E\u30D8\u30EB\u30D7\u3067\u3059\u3002" },
            { "FileChooser.openButton.textAndMnemonic", "OK" },
            { "FileChooser.openButtonToolTip.textAndMnemonic", "\u9078\u629E\u3057\u305F\u30D5\u30A1\u30A4\u30EB\u3092\u958B\u304D\u307E\u3059\u3002" },
            { "FileChooser.openDialogTitle.textAndMnemonic", "\u958B\u304F" },
            { "FileChooser.pathLabel.textAndMnemonic", "\u30D1\u30B9\u307E\u305F\u306F\u30D5\u30A9\u30EB\u30C0\u540D\u3092\u5165\u529B(&P):" },
            { "FileChooser.saveButton.textAndMnemonic", "\u4FDD\u5B58" },
            { "FileChooser.saveButtonToolTip.textAndMnemonic", "\u9078\u629E\u3057\u305F\u30D5\u30A1\u30A4\u30EB\u3092\u4FDD\u5B58\u3057\u307E\u3059\u3002" },
            { "FileChooser.saveDialogTitle.textAndMnemonic", "\u4FDD\u5B58" },
            { "FileChooser.updateButton.textAndMnemonic", "\u66F4\u65B0" },
            { "FileChooser.updateButtonToolTip.textAndMnemonic", "\u30C7\u30A3\u30EC\u30AF\u30C8\u30EA\u306E\u30EA\u30B9\u30C8\u3092\u66F4\u65B0\u3057\u307E\u3059\u3002" },
        };
    }
}

⏎ com/sun/java/swing/plaf/motif/resources/motif_ja.java

Or download all of them as a single archive file:

File name: jre-rt-com-1.8.0_191-src.zip
File size: 8099783 bytes
Release date: 2018-10-28
Download 

⇒ Backup JDK 8 Installation Directory

⇐ JRE 8 rt.jar - org.* Package Source Code

⇑ Download and Use JDK 8

⇑⇑ FAQ for JDK (Java Development Kit)