add Preconditions

.idea/misc.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="EntryPointsManager">
+    <entry_points version="2.0" />
+  </component>
   <component name="NullableNotNullManager">
     <option name="myDefaultNullable" value="android.support.annotation.Nullable" />
     <option name="myDefaultNotNull" value="android.support.annotation.NonNull" />
@@ -34,7 +37,7 @@
     <ConfirmationsSetting value="0" id="Add" />
     <ConfirmationsSetting value="0" id="Remove" />
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_7" default="true" assert-keyword="true" jdk-15="true" project-jdk-name="1.8" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" default="true" assert-keyword="true" jdk-15="true" project-jdk-name="1.8" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/build/classes" />
   </component>
   <component name="ProjectType">

arms/src/main/java/com/jess/arms/utils/Preconditions.java

+package com.jess.arms.utils;
+
+import android.support.annotation.Nullable;
+
+/**
+ * Created by jess on 26/09/2016 13:59
+ * Contact with jess.yan.effort@gmail.com
+ */
+
+public final class Preconditions {
+    private Preconditions() {
+    }
+
+    public static void checkArgument(boolean expression) {
+        if(!expression) {
+            throw new IllegalArgumentException();
+        }
+    }
+
+    public static void checkArgument(boolean expression, @Nullable Object errorMessage) {
+        if(!expression) {
+            throw new IllegalArgumentException(String.valueOf(errorMessage));
+        }
+    }
+
+    public static void checkArgument(boolean expression, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) {
+        if(!expression) {
+            throw new IllegalArgumentException(format(errorMessageTemplate, errorMessageArgs));
+        }
+    }
+
+    public static void checkState(boolean expression) {
+        if(!expression) {
+            throw new IllegalStateException();
+        }
+    }
+
+    public static void checkState(boolean expression, @Nullable Object errorMessage) {
+        if(!expression) {
+            throw new IllegalStateException(String.valueOf(errorMessage));
+        }
+    }
+
+    public static void checkState(boolean expression, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) {
+        if(!expression) {
+            throw new IllegalStateException(format(errorMessageTemplate, errorMessageArgs));
+        }
+    }
+
+    public static <T> T checkNotNull(T reference) {
+        if(reference == null) {
+            throw new NullPointerException();
+        } else {
+            return reference;
+        }
+    }
+
+    public static <T> T checkNotNull(T reference, @Nullable Object errorMessage) {
+        if(reference == null) {
+            throw new NullPointerException(String.valueOf(errorMessage));
+        } else {
+            return reference;
+        }
+    }
+
+    public static <T> T checkNotNull(T reference, @Nullable String errorMessageTemplate, @Nullable Object... errorMessageArgs) {
+        if(reference == null) {
+            throw new NullPointerException(format(errorMessageTemplate, errorMessageArgs));
+        } else {
+            return reference;
+        }
+    }
+
+    public static int checkElementIndex(int index, int size) {
+        return checkElementIndex(index, size, "index");
+    }
+
+    public static int checkElementIndex(int index, int size, @Nullable String desc) {
+        if(index >= 0 && index < size) {
+            return index;
+        } else {
+            throw new IndexOutOfBoundsException(badElementIndex(index, size, desc));
+        }
+    }
+
+    private static String badElementIndex(int index, int size, String desc) {
+        if(index < 0) {
+            return format("%s (%s) must not be negative", new Object[]{desc, Integer.valueOf(index)});
+        } else if(size < 0) {
+            throw new IllegalArgumentException((new StringBuilder(26)).append("negative size: ").append(size).toString());
+        } else {
+            return format("%s (%s) must be less than size (%s)", new Object[]{desc, Integer.valueOf(index), Integer.valueOf(size)});
+        }
+    }
+
+    public static int checkPositionIndex(int index, int size) {
+        return checkPositionIndex(index, size, "index");
+    }
+
+    public static int checkPositionIndex(int index, int size, @Nullable String desc) {
+        if(index >= 0 && index <= size) {
+            return index;
+        } else {
+            throw new IndexOutOfBoundsException(badPositionIndex(index, size, desc));
+        }
+    }
+
+    private static String badPositionIndex(int index, int size, String desc) {
+        if(index < 0) {
+            return format("%s (%s) must not be negative", new Object[]{desc, Integer.valueOf(index)});
+        } else if(size < 0) {
+            throw new IllegalArgumentException((new StringBuilder(26)).append("negative size: ").append(size).toString());
+        } else {
+            return format("%s (%s) must not be greater than size (%s)", new Object[]{desc, Integer.valueOf(index), Integer.valueOf(size)});
+        }
+    }
+
+    public static void checkPositionIndexes(int start, int end, int size) {
+        if(start < 0 || end < start || end > size) {
+            throw new IndexOutOfBoundsException(badPositionIndexes(start, end, size));
+        }
+    }
+
+    private static String badPositionIndexes(int start, int end, int size) {
+        return start >= 0 && start <= size?(end >= 0 && end <= size?format("end index (%s) must not be less than start index (%s)", new Object[]{Integer.valueOf(end), Integer.valueOf(start)}):badPositionIndex(end, size, "end index")):badPositionIndex(start, size, "start index");
+    }
+
+    static String format(String template, @Nullable Object... args) {
+        template = String.valueOf(template);
+        StringBuilder builder = new StringBuilder(template.length() + 16 * args.length);
+        int templateStart = 0;
+
+        int i;
+        int placeholderStart;
+        for(i = 0; i < args.length; templateStart = placeholderStart + 2) {
+            placeholderStart = template.indexOf("%s", templateStart);
+            if(placeholderStart == -1) {
+                break;
+            }
+
+            builder.append(template.substring(templateStart, placeholderStart));
+            builder.append(args[i++]);
+        }
+
+        builder.append(template.substring(templateStart));
+        if(i < args.length) {
+            builder.append(" [");
+            builder.append(args[i++]);
+
+            while(i < args.length) {
+                builder.append(", ");
+                builder.append(args[i++]);
+            }
+
+            builder.append(']');
+        }
+
+        return builder.toString();
+    }
+}